J 2-! 
 
DATE DUE 
 
AN 
 
 EXPERIMENTAL INQUIRY 
 
 INTO THE 
 
 NATURE, CAUSE, AND VARIETIES 
 
 OF THE 
 
 ARTERIAL PULSE; 
 
 AND INTO 
 
 CERTAIN OTHER PROPERTIES 
 
 OF THE 
 
 LARGER ARTERIES, 
 
 IN ANIMALS WITH WARM BLOOD; 
 
 ILLUSTRATED BY ENGRAVINGS. 
 
 BY 
 
 CALEB HILLIER PARRY, M.D. F.R. S. 
 
 MEMBER OF THE COLLEGE OF PHYSICIANS OF LONDON ; 
 MEMBER, AND FORMERLY A PRESIDENT, OF THE ROYAL MEDICAL 
 SOCIETY OF EDINBURGH ; 
 
 HONORARY MEMBER OF THE PHYSICAL SOCIETY OF GOTTINGEN, 
 AND OF THE GEOLOGICAL SOCIETY OF LONDON ; 
 
 ONE OF THE PHYSICIANS TO THE BATH GENERAL HOSPITAL, 
 
 AND PHYSICIAN TO THE CASUALTY HOSPITAL, AND 
 PUERPERAL CHARITY, IN THAT CITY. 
 
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 MUS, PROPTEREA QUOD ET NATURA INEST MENTIBUS NOSTRIS 
 INSATIA BILLS QUiEDAM CUPIDITAS VERI VIDENDI.” 
 
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 PRINTED BY 
 
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 AND SOLD BY 
 
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 ■' QT< A 
 
 
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TO THE 
 
 RIGHT HONOURABLE 
 
 SIR JOSEPH BANKS, BARONET, 
 
 K. G. C. B. 
 
 PRESIDENT OF THE ROYAL SOCIETY, 
 
 &C. &C. &C. 
 
 THE UNWEARIED AND MUNIFICENT PATRON 
 
 OF 
 
 EVERY USEFUL SCIENCE AND ART, 
 
 THIS INQUIRY 
 IS 
 
 WITH JUST RESPECT INSCRIBED, 
 
 BY 
 
 THE AUTHOR. 
 
 FS- 
 
 v J O 
 
 ( % 
 
 C) x 
 
ADDENDA, 
 
 Page 30, 1. 22, after the words “ with regard to the,” infert, “ portion 
 between the first and second ligature in the” 
 
 99. This illustration by Dr. Young, taken from the Hydraulic 
 Ram, I admit only in so far as the finger, when pressing 
 on the first valve, feels the impulse of the lateral 
 current of fluid. 
 
ERRATA. 
 
 Page 103, 1. 4, after “ coincidence” add “ afterwards.’ 1 
 143, 1. 16, dele “ , or annulus venosus.” 
 
Digitized by the Internet Archive 
 in 2016 
 
 https://archive.org/details/experimentalinqu01parr 
 
SYNTHETICAL VIEW 
 
 OF THE CHIEF 
 
 EXPERIMENTS, 
 
 \ 
 
 ON WHICH THE FOLLOWING ANALYSIS 
 IS FOUNDED ; IN THE ORDER IN 
 WHICH THEY WERE MADE. 
 
 EXPERIMENT I» 
 
 September 22, 1814, 8 a. m. 
 fN a Ram, both carotid arteries were laid bare 
 by Mr. George Norman, in the presence 
 of Mr. Coombs, two others of his pupils, and 
 myself. 
 
 Notwithstanding the animal was greatly agi- 
 tated, there was not in either carotid the least 
 appearance of dilatation during the systole of the 
 ventricle, or contraction during its diastole : 
 Nor, except when the: niinal breathed, was there 
 any degree of loco-motion perceived in these 
 arteries, which remained completely quiet and 
 at rest. Nevertheless, when either artery was 
 
 B 
 
2 
 
 Experiments . 
 
 compressed between the finger and thumb, the 
 pulse was very strong and distinct. 
 
 Both arteries were adequately tied by Mr. 
 Norman, each with a single ligature ; after 
 which, the ram stood and walked about well, 
 apparently suffering little inconvenience. 
 
 EXPERIMENT II. 
 
 October 5, 1814, 8 a. m. 
 
 At my desire, and in the presence of the per 
 sons mentioned in the former experiment, Mr. 
 George Norman laid bare the left carotid of 
 a Ram, denuding the artery of its cellular mem- 
 brane. The eighth or vagus nerve was seen 
 attached to it by cellular membrane, on its 
 posterior (upper) side. The pulse, when felt in 
 it, was 100 in a minute ; but no motion whatever 
 was perceptible in the artery to the eye, whether 
 of dilatation or change of place, except that it 
 was slightly moved forwards towards the head, 
 and back again, in respiration, accompanying 
 the trachea. No pulse could be felt in it on 
 mere contact, or even when with the finger it 
 was pressed laterally against the sterno-mastoid 
 muscle ; but when it was taken between the 
 finger and thumb, and so compressed, the pulse 
 in it was sufficiently distinct. 
 
Experiments. 
 
 3 
 
 The diameter of the artery was measured with 
 a pair of fine compasses, and found to be ^.i^dths 
 of an inch. 
 
 A ligature was then made on it, intended 
 merely to half compress it ; and this effect 
 seemed to have been produced at first ; but, on 
 further examination, it was found to have tight- 
 ened itself, so as to prevent all pulsation in the 
 artery beyond it. 
 
 The ligature being now improper for the 
 intended purpose of the experiment, which was 
 to try whether the artery would contract itself 
 beyond the part which was half compressed, it 
 was cut off, and another applied in another part, 
 so as distinctly to allow of a pulsation beyond 
 the ligature. 
 
 In the part immediately before the ligature a 
 very slight movement, of a nature which we 
 could not define, was perceiveable. 
 
 Neither of the ligatures of ram No. I. was 
 come away. He was in good health. 
 
 EXPERIMENT III. 
 
 October 12, 1814. 
 
 This day Mr. G. Norman, in the presence 
 of the before-mentioned persons, cut down 
 upon the femoral artery of a Ram. Without the 
 
 b 2 
 
4 
 
 Experiments. 
 
 aid of a glass, it appeared to all of us perfectly 
 motionless, and void of all dilatation from the 
 systole of the ventricle, which, on pressure 
 against the artery, we found to be 108 times in 
 a minute. A small artery, running nearly 
 parallel to it, and which was possibly the pro- 
 funda femoris, was equally free from loco-motion 
 or dilatation. 
 
 The right carotid was then examined. When- 
 ever the animal ceased for a moment to breathe, 
 or when the artery was drawn upwards out of 
 its place, there was no movement in it of 
 any kind. 
 
 It must, however, be remarked, that from the 
 violent agitation of the animal, there was an 
 almost perpetual loco-motion of the artery du- 
 ring respiration, which we had observed to occur 
 in the two former rams. This motion, however, 
 appeared not to be any proper movement of the 
 artery ; for it alw 7 ays ceased in the short inter- 
 vals when the ram ceased to breathe, and on 
 being accurately and repeatedly reckoned by a 
 ■watch indicating seconds, was found exactly to 
 coincide with the respirations, which were 14 
 in every five seconds, or 168 in a minute ; while 
 the systole of the ventricle, as counted in the 
 same artery, was only 108 in a minute. 
 
Experiments. 
 
 5 
 
 The arteries appeared to be always equally 
 distended in the systole and diastole of the ven- 
 tricle ; and when they were compressed, the part 
 beyond the compression remained just as full as 
 before, though having no pulse. 
 
 The right carotid was tied with a single 
 ligature. 
 
 October 17, 1814. 
 
 This day the ram, in Experiment I. was exa- 
 mined. The ligatures were come away, and 
 the parts wounded were completely healed. 
 
 The ram, of Experiment II. was also exa- 
 mined. The wound appeared to be healed. 
 
 The ram No. III. was also, like the others, in 
 good health. Soon afterwards, the ram No. III. 
 in fighting with No. I. had the ligature on the 
 right carotid torn out, and suffered a considera- 
 ble haemorrhage. Mr. Norman merely put a 
 ligature by means of a needle round the mus- 
 cular and other substances contiguous to the 
 torn spot ; and, the haemorrhage ceasing, left the 
 animal to his fate. 
 
 Subsequently to this period, in 1814, the 
 carotids in one or more Sheep and Rabbits were 
 examined ; but as the results appeared exactly 
 conformable to those above stated, they were 
 
6 
 
 Experiments. 
 
 not recorded. No dilatation of the artery, from 
 the impulse of the blood by the systole of the 
 left ventricle, could, in any case, be discovered, 
 even with the strongest magnifier, the field of 
 which was sufficient to include the whole 
 diameter of the artery. 
 
 EXPERIMENT IV. 
 
 April 20, 1815, 8 a. m. 
 
 This day Mr. George Norman, in the pre- 
 sence of three of his pupils and myself, made the 
 following experiment on a Ram. 
 
 He dissected down to the carotid on the right 
 side. The artery was very distinct. It had no 
 dilatation or contraction whatever ; but had a 
 longitudinal motion backwards and forwards, 
 exactly corresponding with the respirations, so 
 that it was drawn backwards towards the thorax 
 at each inspiration, and returned forwards into 
 its place at each exspiration. 
 
 Its circumference, being accurately measured, 
 was found to be 444 °f an inch ; whence its 
 diameter might be stated as being, in round 
 numbers, about i- of an inch. 
 
 The left carotid being exposed in the same 
 way for exactly 2 *- inches in length, and denuded 
 of cellular membrane as much as possible all 
 
Experiments . 7 
 
 round, was found to be in circumference 4*4 of 
 an inch. 
 
 In this second artery, as in the former, there 
 was a total want of all dilatation and contraction ; 
 but the longitudinal motion, corresponding with 
 respiration, was very conspicuous; and during 
 every violent exspiration, the artery, which, in 
 the part laid bare, was separated from all its ad- 
 hesions, was pushed forwards with such force, as 
 to form a segment of a circle backwards towards 
 the posterior part of the neck, but recovered its 
 longitudinal direction at each inspiration. 
 
 This latter artery was then tied by a single 
 ligature, exactly in the middle of the exposed part. 
 
 EXPERIMENT V. 
 
 June 8, 1815. 
 
 One of the carotids of a Ewe was laid bare by 
 Mr. G. Norman, in the presence of some 
 of his pupils, Dr. Rigby of Norwich, and 
 myself. No motion of the artery could be 
 perceived, except the longitudinal one from 
 respiration before mentioned ; nor could any 
 pulse be felt, except when the diameter of the 
 artery was lessened by counter pressure to that 
 of the finger. 
 
8 
 
 Experiments. 
 
 EXPERIMENT VI. 
 
 July 31, 1815, 3 p. m. 
 
 Present Mr. Soden, surgeon ; Mr. George 
 Kitson, surgeon ; Mr. Coombs; two of Mr. 
 G. Norman’s pupils ; and myself. 
 
 Mr. G. Norman laid bare the left carotid of 
 a small Spaniel Dog; the pulse of which in 
 the femoral artery, after he was laid on the table, 
 and previously to any operation, was 72 in a 
 minute, and considerably irregular. 
 
 The carotid was denuded for more than two 
 inches in length. A nerve (descendens noni ?) 
 and a small vein crossed it, and the vagus and 
 sympathetic nerve ran together in close contact 
 with it. 
 
 After the incision, the pulse was a beat or two 
 slower, but not more irregular than before; the 
 dog being perfectly quiet. A motion in the 
 artery, corresponding with the systole of the 
 ventricle, was very apparent. It was, however, 
 evidently for the most part a longitudinal one ; 
 the artery advancing forw ards towards the head 
 during the systole, and retreating during the 
 diastole. Once the motion appeared to be in 
 some degree lateral, that is, of the whole artery 
 from side to side. It w as, however, evident, 
 after a long' and attentive examination, assisted 
 
Experiments. 
 
 9 
 
 by a strong- lens, that there was nothing like 
 dilatation and collapse, or a change in the dia- 
 meter of the vessel, which always appeared 
 equally full and extended. 
 
 EXPERIMENT VII. 
 
 Immediately after the foregoing experiment, 
 the left carotid was examined in a Ewe ; the 
 neck and head being stretched out during the 
 operation. Here, also, there was no dilatation or 
 contraction, nor was any movement perceived 
 from the systole and diastole of the ventricle ; 
 but a longitudinal movement backwards and 
 forwards from respiration was evident, as in the 
 preceding experiments. 
 
 EXPERIMENT VIII. 
 
 August 2, 1815, 3f p. m. 
 
 In the presence of Mr. Tudor, surgeon, 
 Mr. Coombs, three pupils, and myself, Mr. G. 
 Norman laid bare the carotid of a Ewe, of 
 which the other carotid had been examined, 
 July 31st. 
 
 When the head was stretched out, and the 
 neck forcibly elongated, no movement was per- 
 ceptible in the carotid, except that produced by 
 respiration ; but when the head and neck were 
 
10 
 
 Experiments. 
 
 placed in a more easy posture, so that the caro- 
 tid, dissected from its attachments, became loose, 
 then the systole and diastole of the ventricle 
 were apparent by a movement of the artery, 
 which, to most of us, was perceived to be mere 
 loco-motion in different directions ; as we were 
 absolutely unable to discover, either with the 
 naked eye, or with glasses, any change in the 
 diameter of the artery. Mr. Tudor was not, 
 however, clear that he did not perceive some 
 dilatation, though not, in his opinion, sufficient 
 to produce the phaenomenon of the pulse. 
 
 EXPERIMENT IX. 
 
 The same experiment was immediately after- 
 wards repeated on the carotid, and femoral 
 artery of a Ram, and with the same results. The 
 different movements from respiration, and the 
 action of the heart, were perceivable in both 
 arteries when relaxed ; more especially by the 
 continuance of the movement from the heart, 
 during different times that the animal for a few 
 seconds ceased to breathe. 
 
 EXPERIMENT X. 
 
 August 5, 1815, 3 p. m. 
 
 In the presence of Mr. George Kitson, Mr. 
 Brown, surgeon, Mr. Coombs, three of Mr. 
 
Experiments. 
 
 11 
 
 Norman’s pupils, and myself, Mr. G. Norman 
 exposed the right carotid of the Dog which 
 had been operated on three days before.. 
 
 When the neck was stretched out, the influ- 
 ence of the systole of the ventricle on it was 
 obscure, but apparent when it was bent in a 
 somewhat natural posture, as the dog lay on his 
 left side. This influence consisted of various 
 modes of loco-motion in the artery, such as 
 lateral, forwards and backwards, and longitudi- 
 nal in both directions ; but neither of us could 
 discover, either with the naked eye, or a strong 
 lens, the least change in the diameter of the 
 artery, either of dilatation or contraction. The 
 femoral artery on the same side was at the same 
 time laid bare ; and the same appearances were 
 observed in it as in the carotid. 
 
 The breathing of the dog having been through- 
 out very little hurried, the movement from it 
 was with difficulty discernible. 
 
 EXPERIMENT XI. 
 
 August 11, 1815, 4 p. m. 
 
 Present, Mr. Coombs, two of Mr. George 
 Norman’s pupils, and myself. 
 
 Mr. Norman having laid bare the two caro- 
 tids of a Rabbit, more than half grown, we all 
 
12 Experiments. 
 
 saw in those vessels a movement backwards and 
 forwards, which corresponded with their pulse, 
 but so short that it was not always visible with- 
 out a magnifying glass. The movements, also, 
 were so quick, that it was impossible to count 
 them. We many times viewed them in the sun- 
 shine with a strong lens, but could not perceive 
 the least change in their diameter, whether of 
 dilatation or contraction. No difference in these 
 movements Avas produced by any change of the 
 position of the head. 
 
 The abdominal aorta was then exhibited, and 
 denuded of the peritonaeum for a considerable 
 extent. The respirations were 72 in a minute. 
 We could not, either with the naked eye or the 
 lens, discover in this artery any movement, 
 whether longitudinal or otherwise; though at 
 the same time, when it was pressed by the finger, 
 its pulse was firm and perfectly distinct. 
 
 EXPERIMENT XII. 
 
 August 16, 1815, 6 p. m. 
 
 Examined both carotids of a Rabbit, two-thirds 
 grown. The dissection, as usual, by Mr. Geo. 
 Norman, in the presence of Dr. Dickson, R.N. 
 Mr. Coombs, two pupils of Mr. Norman, and 
 myself. 
 
Experiments. 
 
 13 
 
 There was evidently no dilatation or contrac- 
 tion whatever ; but there were two sets of move- 
 ments; one produced by respiration, and being 1 
 longitudinal and much slower than the other, 
 the movement of the adjacent parts keeping 
 pace with it; the other depending on the systole 
 of the heart, and being generally longitudinal, 
 but occasionally, though rarely, lateral, or even 
 in a certain degree rotatory. All the latter 
 movements were, however, extremely quick 
 and short, so as scarcely to be discoverable with- 
 out a strong lens, and to be by no means capable 
 of being counted. Even the respirations were 
 120 in a minute. 
 
 This was the result of our observations, in 
 whatever posture the animal’s head or body was 
 placed. 
 
 The abdomen was then opened, and the aorta 
 examined. Mr. Norman could not perceive in 
 it any motion whatever, even with the lens ; but 
 Dr. Dickson was not sure that he could not 
 distinguish some trembling of it. There was, 
 however, evidently no dilatation or contraction, 
 though the pulse was strong on pressure. The 
 respirations continued to be 120 in a minute. 
 
14 
 
 Experiments. 
 
 EXPERIMENT XIII. 
 
 August 23, 1815, 3f p. m. 
 
 Present, Mr. Coombs, three pupils of Mr. 
 G. Norman, and myself. 
 
 In a Ram, Mr. G. Norman cut down on the 
 left femoral artery. It had a confused move- 
 ment from respiration, not peculiar to itself, 
 but in common with the rest of the body, from 
 the general agitation which the rise and descent 
 of the diaphragm, and the consequent protrusion 
 and retraction of the abdomen, produced. When, 
 however, the respiration for a while ceased> 
 which was frequently the case, we could easily 
 see the longitudinal motion of the artery, cor- 
 responding with the systole of the left ventricle 
 of the heart. We could not in this experiment 
 decide whether this was elongation of the artery, 
 mere loco-motion, or both. 
 
 The right carotid w as then examined, and 
 was separated from all its adhesions. When the 
 head was stretched out, and the neck straight- 
 ened, the motion chiefly apparent Was the longi- 
 tudinal one from respiration, so often described ; 
 and even when the respiration for a while ceased, 
 the motion from the systole of the ventricle was 
 very obscure. On the other hand, when the 
 neck was bent, and the carotid became by the 
 
Experiments. 
 
 15 
 
 position tortuous, with its convex bend project- 
 ing outwards, each systole increased this con- 
 vexity in a very sensible degree; and the vessel 
 returned to its former state during the diastole of 
 the ventricle. We could not, however, though 
 assisted by lenses, discover any change of dia- 
 meter in either artery. The pulse could not be 
 perceived either in the femoral or carotid, when 
 simply touched with the finger, without compres- 
 sion ; but was evident enough, when, by pressure 
 against a hard substance, the diameter was 
 diminished. 
 
 We now killed the animal by a ligature round 
 the trachea, clear of all the vessels. 
 
 Previously to his being killed, on examining 
 the carotid, we found in it, in one spot, a stricture 
 or contraction of the artery, which had not 
 existed before, and which was not more exten- 
 sive than if a fine piece of twine had been tied 
 round it. About an inch and a half below this 
 spot, where the artery retained its natural size, 
 it was found, by an accurate measurement, twice 
 tried, to be exactly of an inch in cir- 
 cumference. 
 
 Within five minutes after the death of the ani- 
 mal, the same artery being measured as nearly 
 as possible in the same place, was found to be 
 
16 
 
 Experiments. 
 
 in circumference only 444 of an inch ; being 
 thus reduced ^^-nths. The femoral artery was 
 also greatly shrunk in size ; but the degree was 
 not ascertained by actual admeasurement. 
 
 August 24, p. m. 
 
 The carotid artery was again measured, 21f 
 hours after the former admeasurement, and ex- 
 actly in the same spot. It was now found to be 
 in circumference 44-4 °f an inch, or to have 
 gained, since the last measurement, of aninch. 
 
 The process of putrifaetion having begun in 
 the abdomen and dissected thigh of this animal, 
 there can be little reason to doubt that its death, 
 and consequently its loss of tonicity, was total 
 and complete. 
 
 EXPERIMENT XIV. 
 
 September 4, 1815, 34 p. m. 
 
 Present Dr. Charles Parry, Mr. George 
 Kitson, two of Mr. G. Norman’s pupils, and 
 myself. 
 
 Mr. G. Norman exposed the right carotid 
 of a Rabbit, two thirds grown. The respirations 
 were 72 in a minute; and when the head and 
 neck were in a relaxed posture, it was very easy 
 to distinguish the two different movements 
 
Experiments. 
 
 17 
 
 from respiration and tire systole of the ventricle ; 
 the former being much slower than the latter. 
 When the mouth was stretched out in a line 
 with the neck, the latter motion was scarcely 
 perceptible, and only the former was distinctly 
 observable. Both movements were longitudi- 
 nal; and it was well observed by Dr. Charles 
 Parry, that the line of light, on the convex 
 surface of the artery, when viewed with a strong 
 lens, never changed its position ; which could not 
 have been the case, had not the diameter of the 
 artery remained the same. The movement from 
 the systole was very short and quick. 
 
 Mr. Kitson, who had not witnessed many of 
 these experiments, could not feel any pulse in the 
 carotid when he pressed it, unless some hard 
 substance, such as the trachea, was opposed to his 
 finger, so as to reduce the diameter of the artery. 
 
 Mr. Norman for a considerable time rubbed 
 with his finger a portion of the carotid ; but the 
 artery was not dilated by the friction. 
 
 The abdomen was now opened, and the aorta, 
 Undivested of the peritonaeum, was examined, 
 chiefly above the exit of the mesenteric arteries. 
 There was now a very distinct motion from the 
 systole of the ventricle, but none from respira- 
 tion, the exact process of which was easily 
 
 c 
 
18 
 
 Experiments. 
 
 ascertained by the descent and ascent of the 
 diaphragm. This movement of the artery 
 simulated that of dilatation and contraction more 
 nearly than any which I had' ever before wit- 
 nessed ; but since, on farther examination with 
 a powerful lens, it appeared that the artery had 
 at the same time no lateral swell, it was evident 
 that this was not dilatation and contraction, 
 but merely an advance of the whole forwards 
 towards the eye, alternating with a retreat back- 
 wards from it. With this, there was a slight 
 union of the longitudinal motion already so 
 often described, 
 
 EXPERIMENT XV. 
 
 September 7, 1815, 3^ p. m. 
 
 Present Dr. Charles Parry, Mr. Chap- 
 man, Mr. Wood, and Mr. Field, (three of Mr. 
 G. Norman’s pupils,) and myself. 
 
 In the Ram before mentioned, Experiment 
 III. and which was verv fat, Mr. Coombs laid 
 bare the left carotid. We were extremely sur- 
 prised at the great superiority of size in this 
 artery, comparatively with those which we had 
 before examined. It had a very strong motion 
 from the systole of the heart, as the animal lay 
 on his back with the neck relaxed, so that it 
 
Experiments . 
 
 19 
 
 bent itself forwards towards us with every ac- 
 celeration of the current of blood from the 
 systole of the ventricle, and receded during the 
 slower current from the diastole. With this mo- 
 tion there was also a longitudinal one from the 
 same cause, but no lateral enlargement, and 
 therefore no increase of diameter whatever. 
 
 Two measurements of the circumference of 
 this artery were made in the same spot, and ex- 
 actly coincided, giving a circumference of 
 444 of an inch. 
 
 The ram was then killed by a ligature round 
 the trachea only ; the vessels not being included. 
 
 After the animal was dead, at the end of 
 six minutes from the first application of the 
 ligature round the trachea, the carotid was 
 again examined. The decrease of size was 
 extremely conspicuous. Being measured in pre- 
 cisely the same place as before, it Was found to 
 be in circumference only 444 of an inch, ha- 
 ving suffered a diminution of 444 of an inch. 
 
 September 8, 3f p. m. 
 
 The artery being again examined in the same 
 spot, was found to be in circumference 144 °f 
 an inch, which w'as an increase, subsequently to 
 the preceding day, of of an inch* 
 
 c 2 
 
20 
 
 Experiments. 
 
 EXPERIMENT XVI. 
 
 September 13, 1815. 
 
 Present Mr. Coombs, Mr. Norman’s pupils 
 before mentioned, and myself. 
 
 Mr. G. Norman examined the right carotid 
 of a full-grown fat Wether. When the mouth 
 was stretched out, no motion was to be seen in 
 the artery, but the longitudinal one from respi- 
 ration ; but when the artery became somewhat 
 tortuous, from bending the head forwards, the 
 vessel, completely denuded of the contiguous 
 substances, suffered some additional flexion from 
 the systoles of the heart. But there was no per- 
 ceptible movement of dilatation or contraction. 
 The mean of three measurements of the circum- 
 ference of the artery, in the same spot, was .*.*-*. 
 of an inch. 
 
 The left carotid w as now exposed in a similar 
 way ; and one or two attempts were made to 
 confine the blood in a portion of it included 
 between two ligatures ; but it w r as found very 
 difficult to prevent the evacuation of the insu- 
 lated part through some openings w ithin one or 
 other of the ligatures. At last, by straining 
 two ligatures at the same instant, a portion of 
 the artery, of about an inch and a half in length, 
 was left distended w'ith blood, although it had 
 
Experiments. 
 
 21 
 
 evidently contracted itself to a smaller magnitude 
 than when it was first exposed. The circum- 
 ference of this part was found to be 4§4 °f 
 an inch. 
 
 In the part so included, when it was com- 
 pressed between the finger and thumb, there 
 wasan obscure pulse, exactly corresponding with 
 that of the portion before the ligature. 
 
 The included part being now punctured with 
 a lancet, blood flowed from if, but with little 
 force. It being then measured in the same part 
 as before, was found to be in circumference 
 444 °f an inch. 
 
 The sheep was now killed, by opening the left 
 carotid just before the ligature. This was at ~ 
 past five. The animal was five minutes in 
 dying. Ten minutes afterwards, the right ca- 
 rotid being measured in the same point as 
 before, was reduced in circumference to 444 
 an inch. 
 
 The sheep was immediately skinned, and the 
 abdominal viscera removed. 
 
 September 14, Of a. m. 
 
 The right carotid, being’ now measured, was 
 found to be in circumference 444 an inch. 
 
22 
 
 Experiments. 
 
 EXPERIMENT XVII. 
 
 Wednesday, September 27, 3f p. m. 
 
 Mr. Coombs, in the presence of several pupils 
 of Mr. George Norman, and myself, cut down 
 to the right carotid of a stout Ram Lamb in per- 
 fect health, and six months old. 
 
 A ligature was placed round it, but not tight- 
 ened, and the artery was carefully measured 
 before and beyond the place of the ligature. 
 The circumference before the ligature was 444 
 of an inch; that beyond it was 444 of an inch. 
 
 The ligature being then tightly drawn, the 
 artery was again measured in the same spots 
 as before. The circumference before the ligature 
 was 444 an inch ; and beyond it, was 444 of 
 an inch. 
 
 No pulsation could be felt, by any mode of 
 examination, beyond the ligature ; but when 
 the artery was compressed between the finger 
 and thumb, and the pressure was suddenly 
 diminished, the sides of the artery struck against 
 the finger and thumb so as to simulate a pulse. 
 
 About 4 of an inch, or a little more, beyond 
 the part where the ligature was made, a branch 
 was given off by the carotid. 
 
 The left carotid artery w as now exposed, and 
 as quickly as possible tied. 
 
Experiments 23 
 
 Scarcely any blood flowed during- the ope- 
 rations. 
 
 When the lamb was taken off the table, he 
 seemed to be greatly distressed. He attempted 
 several times to rise, but ineffectually ; at last 
 he got on his feet, his Avhole body and limbs 
 trembling, and the latter bending under him, so 
 that he stood with difficulty, and in attempting 
 to walk, di’agged his legs after him, and soon 
 fell on his right side. His head was bathed with 
 a cold sweat ; and at various times, for half an 
 hour, he got up and ineffectually repeated his 
 attempts to walk, in the manner before described. 
 
 He was at length taken away and laid on 
 straw, from which, when we last saw him, which 
 was three quarters of an hour after the com- 
 mencement of the operation, he had made no 
 farther efforts to rise. 
 
 On the afternoon of the 28th, he stood, but 
 with difficulty ; shewing little sensibility when 
 he was approached or even touched ; and his 
 nose being always directed downwards towards 
 the ground. He had tried to take food ; but 
 after he had chewed it, dropped it out of 
 his mouth. 
 
 From this period he eat nothing, but thick 
 barley gruel was once or twice poured down his 
 
24 
 
 Experiments. 
 
 throat. He stood always in one place, with his 
 head to the ground, apparently unable to see, 
 and shewing no fear, or other marks of percep- 
 tion, either when he was touched, or a violent 
 noise was made close by his ear. 
 
 On the morning of the 3d of October, he died. 
 
 He was dissected by Mr. Coombs the next 
 morning. No nerve had been included in either 
 of the ligatures. The parts round the arteries 
 operated on were healed, and no inflammation 
 existed within or without the vessels ; both of 
 which had coalesced at the points of ligature, 
 apparently by means of coagulated iibrine; from 
 which, in each, there was a conical coagulum of 
 blood of 1. of an inch in length before the liga- 
 ture only, and unattached to the serous coat. 
 
 EXPERIMENT XVIII. 
 
 Immediately after the former experiment, 
 both carotids were carefully examined, and 
 afterwards tied, each with a single ligature, at 
 the same instant, in a Ham two years old. 
 
 He struggled a great deal during the tight- 
 ening of the ligatures ; but soon afterwards, 
 being taken oft' the table, he quickly raised 
 himself on his feet, and having for a few 7 seconds 
 stared around in a confused manner, ran out of 
 
Experiments. 
 
 23 
 
 the room into the yard with great strength, and 
 without any apparent inconvenience. 
 
 No pulse was perceived in either artery be- 
 yond the ligature ; nor could any dilatation or 
 contraction from the systole and diastole of the 
 left ventricle be observed. 
 
 EXPERIMENT XIX. 
 
 October 2, 1815, 3 p. m. 
 
 Mr. Coombs, in the presence of three of 
 Mr. G. Norman’s pupils, and myself, examined 
 the left carotid of a Ram, two years and half 
 old, whose right carotid had been examined on 
 the 2d of August. 
 
 The circumference of the artery, at the ex- 
 tremity of the incision next the heart, was 
 444 of an inch : and f an inch farther was 
 of an inch. It was, however, certain, that much 
 cellular membrane was left attached to the ex- 
 ternal coat of the artery. 
 
 A ligature was then firmly made between thes e 
 two spots so measured. There was an exceed- 
 ingly strong pulse in the artery immediately 
 before the ligature, which appeared to move a 
 short distance forwards at each systole of the 
 heart, and to retreat during its diastole. 
 
26 
 
 Experiments. 
 
 A slight pulsation was also perceptible to the 
 finger, immediately beyond the ligature ; but it 
 ■was evidently produced by the motion of elonga- 
 tion or advance of the artery before the ligature, 
 from the shock given by the blood; for it w ? as 
 felt only on the side of the finger and thumb 
 next the ligature, but no farther. A little 
 farther onwards, as half an inch, the impulse 
 was only now and then perceivable, and then 
 only on very slight contact ; being wholly lost, 
 if any greater pressure was made on the artery. 
 
 Another ligature was now firmly applied, at 
 the distance of li of an inch farther. The cir- 
 cumstances as to the pulsation between these 
 ligatures were exactly the same as in the for- 
 mer trial, just related. 
 
 No movement of any kind could be felt 
 beyond the second ligature. 
 
 A third ligature was made at the distance of 
 £ of an inch from the second. The pulsation 
 first described was now felt between the two 
 first ligatures, with the same modification as 
 before ; except that the pulse before the first 
 being- now somewhat less strong’, that immedi- 
 ately beyond it was proportionably weakened. 
 
 Still no pulse existed beyond the second liga- 
 ture. The portion of the artery between the 
 
Experiments. 
 
 27 
 
 first and second ligature was now punctured, 
 and the blood squeezed out of it ; notwithstand- 
 ing - which, it g-ave the sensation of pulsation 
 precisely in the manner first described, that is, 
 of an impulse only against the side of the finger 
 and thumb next the first ligature, when they 
 were brought very near it ; but in no degree 
 along the compressing surfaces. 
 
 Hence it was evident, that it was merely a 
 longitudinal stroke, continued on from the free 
 portion of the artery above, and acting in a me- 
 chanical manner, but by no means arising from 
 any dilatation of the empty portion of the artery 
 which was so felt. In this instance, also, the 
 longitudinal advance and retreat of the ligature, 
 corresponding with the increase and diminution 
 of impulse during the systoles and diastoles of 
 the heart, were sufficiently perceivable even 
 by the naked eye. 
 
 A ring of the artery between the two first 
 ligatures, being now cut off at the point nearly 
 corresponding to that last measured, was found 
 to be extremely contracted, and on being opened 
 and laid flat, was found to measure transversely, 
 on its outer coat, only 244 °f an inch. It must, 
 however, be remarked, that it had been conside- 
 
28 
 
 Experiments. 
 
 rably denuded of its cellular membrane, subse- 
 quently to the former measurement. 
 
 Nearly the whole of the artery between the 
 first and third ligatures was now cut away; and 
 the wound, which was a very long one, was 
 sewed up. 
 
 In this sheep, all the parts about the left 
 carotid appeared much more vascular than 
 usual, and discharged a considerable quantity of 
 blood from cut vessels. One or two pretty large 
 branches also arose from the carotid between the 
 first and second ligatures. These branches were 
 tied, before the examinations above described 
 were made. 
 
 The right carotid, which had been exposed, 
 but not tied, in August, was now examined 
 by Mr. Coombs, and tied with a single 
 
 ligature. 
 
 © 
 
 EXPERIMENT XX. 
 
 October 3, 1815, 3 p. m. 
 
 Mr. G. Norman, in the presence of Dr. 
 Charles Parry, Mr. Coombs, Mr. Sewell, 
 veterinary surgeon, four of Mr. Norman’s 
 pupils, and myself, laid bare for several inches 
 the right carotid artery of a large old Horse, 
 intended for the slaughterer. 
 
Experiments. 
 
 29 
 
 The pulse, both before and after the horse 
 was thrown, was 48 in a minute. 
 
 The circumference of the artery was ±44 of 
 
 an inch. 
 
 Its movement was very long* and carefully 
 examined. 
 
 No person present could discover the least 
 degree of dilatation or contraction of the artery, 
 during the systole and diastole of the heart. 
 
 No motion of a longitudinal kind occurred 
 from respiration. In reality, the artery appeared 
 altogether quiescent, except during, and for 
 two or three seconds after, a violent struggle ; 
 in which case the artery once or twice bent 
 itself outwards during the systole, and re- 
 turned during the diastole. Then the artery 
 became again quiescent, and without motion, as 
 before, even when examined with a strong- lens. 
 
 In order still farther to investigate whether 
 there was any elongation, or longitudinal mo- 
 tion, of the artery, white thread was slightly 
 wound round it in two places ; but we could 
 not discover any change of place, whether ab- 
 solute or relative, in these threads. 
 
 A ligature was then firmly made on the 
 artery. A slight pulsation was perceivable 
 beyond the ligature, just as in the ram in the 
 
30 
 
 Experiments. 
 
 preceding' experiment ; that is, when the artery 
 was held between the finger and thumb, there 
 was an impulse against that side of those parts 
 which was next the ligature, but no perceptible 
 effort at dilatation farther on between the thumb 
 and finger. This phenomenon occurred to a 
 greater distance from the ligature in this ex- 
 periment, than in the ram in the preceding one. 
 
 A longitudinal movement was now observable 
 in the artery beyond the ligature. When, 
 however, the extent of movement was tried, by 
 placing a piece of small thread across the artery, 
 so as to correspond, during the diastole of the 
 heart, with another piece placed on an adjacent 
 muscle, which was motionless, the advance of 
 the artery, during the systole of the heart, was 
 not greater than the diameter of the thread. 
 
 A second ligature being made, an inch be- 
 yond the first, an impulse was capable of being- 
 felt beyond both the first and second lig-ature, in 
 the maimer already mentioned, and just as was 
 described with regard to the ram in the prece- 
 ding experiment, except that it extended to a 
 create r distance. 
 
 o 
 
 A third ligature was now applied, more dis- 
 tantly from the second than the second from 
 the first. The phenomena, as to impulse, were 
 
Experiments . 
 
 31 
 
 precisely the same as with regard to the two 
 former ligatures ; extending’ themselves beyond 
 the third lig’ature. All the ligatures were plainly 
 perceived to move forwards at each systole of 
 the heart, and to return back daring the diastole. 
 
 The part included between the first and 
 second ligature was punctured with a pair of 
 scissars ; but serum alone flowed out. A full 
 hour had elapsed from the time of the second 
 ligature. 
 
 The part between the second and third liga- 
 ture was now punctured and entire blood 
 flowed from the wound. This last ligature 
 had not been made more than a quarter of 
 an hour. 
 
 The impulse was felt, just as before, beyond 
 the second and third ligatures ; and the first, 
 second, and third, were affected by the systole 
 and diastole of the heart, as before the punctures 
 had been made. 
 
 The artery being now measured in the same 
 spot as before, which was a little before the 
 puncture between the second and third ligatures, 
 was found to be in circumference only 144 of 
 an inch. 
 
 The horse was then (44 p. m.J killed, by 
 opening the left carotid artery. 
 
32 
 
 Experiments. 
 
 During these experiments, the head of the 
 horse was always in precisely the same situation 
 with regard to his neck, as in an ordinarv 
 walking attitude. 
 
 The carotid being measured the next moraine* 
 at 9 o’clock, was found to be in circum- 
 ference Af-I of an inch. 
 
 In the space between the first and second 
 ligatures, there were three small clots of black 
 coagulated blood. 
 
 During the dissection down to the artery, a 
 very minute branch springing from the carotid 
 being divided, the blood sprang out to the dis- 
 tance of eight feet. 
 
 EXPERIMENT XXI. 
 
 October 6, 1815, of p m. 
 
 The right carotid of a Horse was laid bare by 
 Mr. Coombs, in the presence of Mr. Sewell, 
 two of Mr. G. Norman’s pupils, and myself. 
 
 This horse was considerably stronger than the 
 former. ITis pulse, after he had been thrown, 
 was 52 in a minute ; and during the dissection of 
 the parts, previously to reaching the artery, a 
 good deal of blood flowed. 
 
 The pulse was now, at a proper time after 
 his having ceased to struggle, 72 in a minute. 
 
Experiments. 33 
 
 and the respiration 24, with grunting or roaring 
 exspirations. 
 
 The circumference of the artery, in a given 
 part, was 444 an inch. 
 
 The head was placed in an easy and natural 
 posture. We could not discover the smallest 
 dilatation or contraction of the artery from the 
 systole and diastole of the ventricle ; but having 
 placed on it a strait piece of white waxed thread 
 in a line with another, on a stationary spot near, 
 we perceived that the former line was protruded 
 beyond the latter, at each systole of the heart, 
 about one and a half time’s the diameter of the 
 thread which was stationary ; and this distance, 
 on accurate measurement, appeared to be about 
 .Jjv of an inch. 
 
 When the artery was firmly compressed be- 
 tween the finger and thumb of one person, a 
 faint sensation of impulse could be perceived 
 by another person, beyond the pressure, in the 
 manner described, with regard to portions in- 
 cluded between ligatures, in the last experiment. 
 
 In this, as in other experiments, when the 
 neck was considerably bent, the carotid, where it 
 was separated from its attachments, rose in a 
 curve outwards at each systole of the ventricle, 
 
 © 
 
$4 Experiments. 
 
 He was now, at half-past five p.m., killed, by 
 opening the left carotid artery. 
 
 Soon after he had ceased to move, the risrht ca« 
 rotid was measured, in the spot before examined, 
 and found to be 4§4 of an inch in circumference. 
 
 On the 7th, at 9 a. m. the circumference of 
 the artery, in the same spot, was 444 of an inch. 
 
 This horse laboured under no thoracic disease. 
 
 EXPERIMENT XXII, 
 
 October 11, 1815, 8f a. m. 
 
 Mr. Coombs, in the presence of Mr. Chap- 
 man, and myself, laid bare both carotids of a 
 Ewe, If year old. 
 
 The left carotid was tied with two ligatures, 
 exactly one inch asunder. No pulsation what- 
 ever could be perceived, either between them, or 
 beyond the second ligature. The artery was 
 then cut through half way between the liga- 
 tures, and the blood sprang out. to a considerable 
 distance from the vessel. The ends of the ar- 
 tery now immediately retracted themselves ; 
 and the distance between the ligatures, being 
 measured, was found to be 144 °f an inch. 
 
 The extremities being now carefully exami- 
 ned, we saw the ligature next the heart propelled 
 longitudinally forwards at each systole of the 
 
Experiments . 
 
 85 
 
 ventricle, and retreat during - the diastole. The 
 more distant ligature also advanced towards the 
 former by a retrograde motion, so also as to 
 correspond with the systoles; but with this diffe- 
 rence, that the advance was less in degree, and 
 always a sensible, but extremely short, space 
 of time after that of the other portion. The 
 difference in time was indeed so small, that the 
 advance of the more distant portion seemed to 
 have taken place, before the retreat of the near 
 portion was sensibly begun. No other movement 
 of the artery, besides the longitudinal one, was at 
 all perceptible. 
 
 During these observations, the neck of the sheep 
 was always stretched in the same degree. 
 
 A small ring was cut off from the farther 
 extremity of the artery. 
 
 The carotid on the right side was now tied 
 with one ligature. 
 
 The ewe did not seem to be in any way ma- 
 terially affected by these operations ; but died 
 two or three days after, from inflammation and 
 suppuration about the left side of the trachea. 
 In the artery on the right side, there was little 
 appearance of external inflammation round the 
 tied part of the artery ; in which, before the 
 
 D 2 
 
36 
 
 Experiments. 
 
 ligature, there was a coagulum of blood, of about 
 an inch in length, but none beyond the ligature. 
 
 EXPERIMENT XXIII. 
 
 •>« October 12, 1815, 34 p. m. 
 
 Mr. Coombs, in the presence of Mi\ George 
 Norman, Mr. Chapman, Mr. Hunt, and 
 myself, laid bare the two carotids of a Ewe, 24 
 years old. 
 
 The ewe was very small. The circumference 
 of the right carotid was 444 of an inch. 
 
 The left carotid was then tied with a sinale 
 ligature. Five minutes afterwards, the right 
 carotid, being again measured in the same place 
 as before, was in circumference 444 °f an inch. 
 
 The right carotid was now tied with a single 
 ligatui'e ; and, a few minutes afterwards, ap- 
 pearing to have shrunk, was again measured half 
 an inch before the ligature, and found to be in 
 circumference exactly 444 of an inch, as before 
 the tying of the opposite artery. 
 
 The left carotid, appearing to be still more 
 reduced in size, was measured before the liga- 
 ture, and found to be only 444 °f an inch in 
 circumference. 
 
 This ewe, at the time, suffered little apparent 
 inconvenience from the ligatures ; but died on 
 
Experiments. 
 
 37 
 
 the morning of October 14. The evident cause 
 of death was inflammation, which had spread 
 itself to all the adjoining parts. The parts tied 
 had, on both sides, coalesced. In the left carotid 
 there was, before the ligature, a thrombus of 
 about half an inch in length ; but neither any 
 coagulum, nor even blood, in the artery beyond 
 the ligature. 
 
 On the risrht side there was a thrombus both 
 before and beyond the ligature ; that beyond 
 being much shorter and smaller than that before. 
 Here also the artery, beyond the farther throm- 
 bus, was empty of blood. 
 
 The tied part was on neither side surrounded 
 either by blood orfibrine; and the artery had not 
 coalesced with the adjacent cellular membrane. 
 
 EXPERIMENT XXIY. 
 
 October 14, 1815, 8t a. m. 
 
 In the presence of Mr. Chapman, Mr. 
 Wood, and myself, Mr. Coombs laid bare both 
 carotids of a Ewe. 
 
 The circumference of the left carotid was 
 £44 of an inch ; of the right £££. 
 
 After the left carotid had been denuded about 
 half an hour, it appeared so contracted for some 
 
38 
 
 Experiments , 
 
 length about the middle of the exposed portion, 
 as to induce us to measure it. It was in circum- 
 ference only .144 of an inch. The parts above 
 and below, W'hich were only just laid bare, ap- 
 peared proportionably increased in size. The 
 circumference of the artery half an inch beyond, 
 being measured, was 444 of an inch. While we 
 were about to measure the portion before the 
 contracted part, we found it in this short space 
 of time so reduced, that we desisted from 
 our purpose. 
 
 The left carotid was then tied beyond the 
 measured part. 
 
 Twelve minutes afterwards, the right carotid, 
 measured in the same spot as before, was found 
 to be in circumference 444 of an inch. 
 
 The pulse in the left artery, before the liga- 
 ture, w 7 as strong and distinct ; but w r as not 
 perceptible beyond it, except faintly, when the 
 finger pressed against the ligature. The lon- 
 gitudinal advance, during the systole of the 
 ventricle, was scarcely discernible, 
 
 The animal was then blooded in the left 
 jugular vein in the following quantities by 
 measure, and with the following effects ; 
 
Experiments. 
 
 89 
 
 I, 
 
 * l 
 
 
 8 
 
 
 1 
 
 iee 
 
 4 09 ' 
 
 ISO 
 
 TVS' 
 
 43S 
 
 TTT 
 
 4 3 5 
 TVS' 
 
 iwcft- 
 
 ( Circumference of the right carotid after 
 the bleeding, - 
 
 Pulse in the carotid good. 
 
 { Circumference - 
 
 Pulse weaker, 
 
 { Circumference - 
 
 Pulse as before. 
 
 /'Circumference of the right carotid - 
 J Pulse slower, and much the same as 
 to apparent strength, but more 
 I jerking, and the longitudinal move- 
 ment stronger. 
 
 Circumference - - - - 
 
 Blood flowed very slowly. Pulse 
 weaker. Jerking increased. 
 Circumference - 
 
 The artery easily compressible. 
 
 The jerking less, and the pulse very 
 weak, and to be felt only on that 
 side of the finger and thumb which 
 was nearest the heart. 
 
 ( Circumference - 
 
 \ Pulse quicker, and very weak. 
 /■Circumference - 
 
 \ Blood required to be rubbed out of 
 the vein. Pulse very quick, small 
 and weak. 
 
 4 4 4 
 
 W 5 * 
 
 4 0 3 
 
 TVF 
 
 I 9 » 
 
 4’Vfc 
 
 8 <S H 
 
 HrVST 
 
 
40 
 
 Experiments. 
 
 Oz. 
 
 Inch. 
 
 7 X 
 
 • o. 
 
 £ Circumference immediately after death 
 Convulsive and stertorous respiration 
 now occurred, and the animal dying-, 
 no more blood could be obtained. 
 Circumference about five minutes after 
 death, - 
 
 
 I 6 © 
 
 '4-0'S- 
 
 2. I 3 
 4 6 "O' 
 
 Ditto 
 
 - 
 
 - ten minutes after death 444 
 
 Ditto 
 
 
 - 4f hours after death 444 
 
 Ditto 
 
 - 
 
 - 11 f- hours after death 444 
 
 Ditto 
 
 - 
 
 - 23 hours after death 444 
 
 Ditto 
 
 - 
 
 - 28f hours after death 444 
 
 Putrifaction had now begun. 
 
 EXPERIMENT XXV. 
 
 October 24, 1815, 8f a. m. 
 
 Present Mr. Chapman, Mr. Wood, Mr. 
 Salmon, and myself. 
 
 Mr. Coombs opened the left side of the tho- 
 rax of a Rabbit^ so as to exhibit the aorta, 
 just beyond the curvature. 
 
 The lung on that side was perfectly col- 
 lapsed on the apex of the heart, the motions of 
 which were very distinct. As the apex shifted 
 its place at each systole of the ventricle, the lung 
 was strongly moved with it, and returned to 
 its place at the diastole. The aorta was 
 
Experiments. 
 
 41 
 
 clearly seen, in a strong 1 sunshine, for a full inch 
 and a half in length. For some minutes it had 
 no apparent movement; but afterwards, as the 
 animal approached towards death, a very slight 
 one, scarcely distinguishable without a strong 
 magnifier. This movement was longitudinal, 
 and sometimes a little lateral, on one side only; 
 but never in any degree that of dilatation or 
 contraction. It exactly accorded with the 
 systole of the heart, which was slow and distinct. 
 In a short time the animal died ; immediately 
 on which the aorta became very sensibly dimi- 
 nished in diameter ; but as the heart con- 
 tinued to beat, a very slight longitudinal motion 
 Still remained, corresponding with the systole, 
 
 EXPERIMENT XXVI. 
 
 October 25, 1815, 8f a. m. 
 
 Present Mr. Chapman, Mr. Wood, Mr. 
 Salmon, and myself. 
 
 Mr. Coombs laid bare the right carotid of 
 a Ewe. 
 
 Its circumference was 444 - of an inch ; but it 
 almost immediately shrunk through the whole 
 space which was exposed, so as to become in 
 circumference only -LLL of an inch. At the same 
 time a portion of the artery, before the contracted 
 
42 
 
 Experiments. 
 
 part, and which had been more recently exposed, 
 was 444 of an inch. 
 
 The pulse in the dilated part was very strong 
 and full ; that in the contracted part very weak 
 and soft. 
 
 The shrunk part being now farther reduced by 
 a ligature of 444- of an inch in length, the pulse 
 beyond the ligature was very faint and weak, 
 and still very strong in the dilated part before it. 
 
 The ligature being removed, we were about 
 to measure the dilated part, but found that it 
 also had begun to shrink. 
 
 The left carotid, being now exposed, appeared 
 evidently much larger than the right ; but im- 
 mediately contracted itself, so as to defeat our 
 intention of ascertaining its enlargement by 
 measure. 
 
 On re-examining the right carotid, we now 
 found it to be again visibly enlarged. It proved 
 to be in circumference 444 of an inch ; but 
 during the measurement, began to shrink, and in 
 a few seconds, appeared to be as small as before. 
 
 The pulse was now 94 in a minute ; and the 
 respiration 42, and irregular. 
 
Experiments. 
 
 43 
 
 EXPERIMENT XXVII. 
 
 December Jl, 1815, 9i p. m. 
 
 Mr. Coombs, in the presence of Mr. Chap- 
 man, Mr. Wood, and myself, laid bare the 
 right carotid of a small Ewe. 
 
 Its circumference was of an inch. 
 
 The left carotid was then exposed, and being 
 tied with packthread in two places distant from 
 each other, so as to intercept the flow of blood, 
 but not break the internal and middle coat, an 
 opening was made between the ligatures, with 
 a view to introduce a small goosequill longitu- 
 dinally into the artery. It had, however, so 
 shrunk by having its blood evacuated, that the 
 quill could not be made to pass up it. A crow 
 quill was then introduced, but was not suffi- 
 ciently large to fill the artery ; so that, when the 
 farthest of the ligatures was loosened, the blood 
 flowed out through the wounded part of the 
 artery. The coats of the artery being firmly 
 tied on the quill just above and below the 
 wound, the ligature nearest the heart was remo- 
 ved. The pulse before the quill was good, but 
 none could be perceived beyond it. 
 
 This experiment, however, is inconclusive, not 
 only from the smallness of the quill, but be- 
 
44 
 
 Experiments. 
 
 cause, when it was removed, the blood was 
 found to have coagulated in it. 
 
 Three firm ligatures having been made round 
 the artery, of which one was on each side of the 
 part containing the quill, and the third beyond 
 the second, the ligatures round the quill were 
 removed, and the quill itself taken out. 
 
 The distance between the first and second 
 ligature was found to be 444 °f an inch. The 
 artery being then cut through between the se- 
 cond and third ligatures, the two ends immedi- 
 ately retracted. The distance between the 
 first and second ligature being now a second 
 time measured, was only 444 °f an inch. 
 
 Professional avocations prevented the farther 
 prosecution of the experiment at this time. 
 
 December 12, 1815, 9f a. m. 
 
 The parts incumbent on the right carotid were 
 found to have in some degree united. 
 
 The artery, being again exposed, was mea- 
 sured as nearly as possible in the same spot as 
 on the preceding day, and found to be in cir- 
 cumference 444 of an inch. This part, however, 
 appeared to be considerably less than the ad- 
 jacent portions of the artery ; and the pulse in 
 
Experiments . 4-5 
 
 it was much weaker and softer than in the more 
 dilated portion immediately before it. 
 
 The ewe was then blooded from the left 
 jugular vein, with the following- effects on the 
 circumference and other circumstances of the 
 carotid artery, the action of the heart, and the 
 respiration : 
 
Circumference 
 
 of the Artery. Pulse. Respiration. 
 
 46 
 
 Experiments. 
 
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[ 47 ] 
 
 ON THE 
 
 1 
 
 STRUCTURE OF ARTERIES, 
 
 THE larger arteries consist of three coats, of 
 which the innermost is smooth within, and thoug h 
 very thin, is strong. Of the three it is said to 
 be the least extensible ; yet, in the living animal, 
 it is evidently capable of bearing', without injury, 
 a considerable degree of stretching. This coat 
 is usually called Cuticular ; but it has certain 
 properties in common with peritonaeum and 
 other serous membranes ; especially that of 
 occasionally secreting, from inflammation, albu- 
 men or fibrine. 
 
 The next, or middle coat of arteries, is the 
 Fibrous ; which, from certain vital properties, 
 has usually been considered as muscular. It 
 must, however, be observed, that according- to 
 that accurate chemist Berzelius, fibrine, which 
 forms a constituent part of muscle, and even of 
 intestine, which has muscular powers, is not dis* 
 
48 On the Structure of Arteries . 
 
 coverable in the coats of arteries. A similaf 
 conclusion has been formed, from chemical 
 analysis, by Dr. Young. 
 
 This middle or fibrous coat is attached to the 
 inner by very thin cellular substance, which 
 seems to be the seat of those bony lamellae, so 
 often found in the larger arteries, and which 
 consist of phosphate of lime. 
 
 Immediately without the fibrous coat is the 
 Cellular ; which appears to be little more than 
 consolidated cellular substance, gradually losing 
 itself in a looser tissue of the same materials, 
 which sometimes forms a sheath, including, not 
 only the artery, but other near and important 
 parts. 
 
 This is the general structure of those arteries, 
 which are sufficiently large to become objects of 
 accurate examination. 
 
 All these coats have their proper vessels, 
 carrying either blood or colourless fluids. The 
 serous coat usually exhibits the latter kind, 
 while the others are more conspicuously furnished 
 with those which convey red blood. During 
 life, however, the cellular coat of arteries is so 
 opake, that the blood circulating in its vessels 
 is scarcely seen ; but if a piece of an artery be cut 
 out of a living animal, and suffered to drv. it 
 
Oil the Structure of Arteries. 
 
 49 
 
 becomes more or less red, probably from the 
 transparency, which its substance acquires from 
 that desiccation. 
 
 The arteriae arteriarum are rarely, if ever, 
 derived from the trunks which they surround; 
 but are minute ramifications of those which are 
 more remote. 
 
 The fluids, effused by these vessels, are capa- 
 ble of being' absorbed by lymphatics; with 
 which, therefore, the coats themselves must be 
 copiously supplied. 
 
 Arteries are also furnished with nerv es, derived 
 from the system of the ganglia. 
 
 G 
 
[ 50 J 
 
 ON THE 
 
 POWERS OF ARTERIES. 
 
 ARTERIES are usually supposed to be en- 
 dowed with a capacity of motion derived from 
 two sources. 
 
 The first is Elasticity ; a merely mechanical 
 power, in consequence of which, when forcibly 
 distended, compressed, or elongated, they spon- 
 taneously return to a mean state, as soon as the 
 force is removed. So when an artery is stretched 
 beyond a certain length, it is said to resume its 
 former state by elasticity alone. A similar power 
 tends to contract it, when it is forcibly dilated, 
 and to expand it into its usual cylindrical form, 
 when it has been forcibly compressed. 
 
 The second is a vital faculty, presumed wholly 
 to reside in the middle or fibrous coat ; which 
 has, therefore, been denominated muscular. 
 
On the Powers of Arteries. 
 
 51 
 
 I have already remarked, that this coat is des- 
 titute of fi brine, which has been supposed to be 
 essential to the composition of muscle ; whence 
 the learned author last quoted infers, that 
 the only power of dilatation and contraction in 
 arteries is derived from their elasticity. Al- 
 though, however, as Bichat has rightly ob- 
 served, parity of structure implies parity of 
 function, it would be highly rash to assume the 
 converse of that proposition, and to assert, that 
 muscular power exists no where but in muscular 
 fibres, or in substances containing fi brine. 
 That question should be solved, not by any pre- 
 sumed analogy, but by a direct observation of 
 facts ; and into these and other properties of 
 arteries, it is the object of this work, by experi- 
 ment, to inquire. 
 
 With regard to the vital power of the middle 
 or fibrous coat of arteries, physiologists have 
 generally agreed, that it acts merely in the 
 direction of the circumference; in consequence 
 of which, the light, or calibre, is diminished 
 when it operates, and to a certain extent in- 
 creased, when it no longer acts. The first 
 case, therefore, implies a shortening, and the 
 second an elongation, of these fibres. 
 
52 
 
 On the Powers of Arteries. 
 
 This power is, however, so far different from 
 that, which, in muscles, is called Irritability, that 
 an artery suffers no degree of contraction from a 
 great variety of chemical and mechanical agents, 
 called Stimuli ; for none of these substances, 
 applied to any part of an artery, wdl cause it 
 to contract. Neither is an artery capable of 
 being thus acted on by what is called the Will. 
 
 The faculty in question seems more similar 
 in its pheenomena to that which, in muscles, has 
 been called Tonicity ; and which implies a 
 mean state of contraction, existing during health, 
 and capable of being increased by certain causes, 
 and of being diminished or lost by certain dis - 
 eases, as hemiplegia, &c. 
 
 In arteries we see this faculty carried to a 
 great extent, even to the obliteration of their 
 cavity; so that in cases in which they cease to 
 convey blood, as in those of ligatures, or of the 
 eanalis arteriosus, & c. they become imper- 
 vious cords. 
 
 Bichat has given to this power the name of 
 Contractiiite par defaut d' extension, and consi- 
 ders it as independent of life. 
 
 It is, however, certain, that the contraction of 
 an artery, to the extent of the coalescence of 
 its parietes, takes placp during life only; and 
 
53 
 
 On the Powers of Arteries. 
 
 I shall hereafter endeavour to shew, that it not 
 only does not exist after total death, but is ac- 
 tually counteracted by certain powers, which 
 preponderate during- that state. 
 
 Hence I havejudg'ed it convenient to give 
 this faculty of vital contraction the name ot 
 Tonicity. 
 
 With regard to the term itself, I wish to be 
 understood as using it to signify, not a cause, 
 but an assemblage of phaenomena, so like, that 
 when the word is employed respecting one of 
 these phaenomena, it serves to recall to the mind 
 the chief phaenomena comprehended under it. 
 This, so far as I can see, is the only purport ot 
 all other abstract terms; which often include 
 many objects, in various respects extremely 
 dissimilar, but agreeing in certain assignable 
 properties. Thus the term Animal comprehends 
 not only an elephant, but a thrush, a minnow, 
 a polypus, and a flea. If, however, any one 
 shall discover an important difference between 
 these phenomena, and shall assign them, seve- 
 rally or collectively, more distinctive, and there- 
 fore better denominations, he is doubtless at 
 liberty to employ them. 
 
 Mr. Hunter has attempted to demonstrate 
 the existence and degree of tonicity in arteries 
 
54 
 
 On the Powers of Arter ies. 
 
 in the following way. In a horse, bled to death, 
 he cut off rings of various arteries, and having 
 slit them in the longitudinal direction of the 
 vessel, measured their transverse length, as they 
 were gently laid flat. Having’ then stretched 
 them out in the same transverse direction, so as 
 to overcome their vital or tonic power, he 
 allowed them to contract by their elasticity ; 
 and, having again measured them as before, 
 judged-that the difference between their present 
 and first length was the measure of their tonicity.* 
 To this and all other similar modes, there 
 seems to be an d priori objection. If the con- 
 traction by tonicity, or muscular power, is the 
 result of life, we should be disposed to conclude, 
 that, as soon as the parts had totally lost that 
 faculty, the moving fibres would relax them- 
 selves, and recover their former length, espe- 
 cially when acted on by the elongator, or elastic 
 cellular coat. If, also, we admit, that a ring of 
 an artery, so treated, still retains some degree of 
 vital power, it is evident, that as no rule can be 
 assigned for the sum existing at any given period 
 after apparent death, no conclusion can be 
 formed as to that, which, in any case, existed 
 during life. Hence this mode of calculating the 
 * Treatise on the Blood, &c. p. 124, 125, 1 2(5. 
 
On the Powers of Arteries. 
 
 55 
 
 tonicity of arteries, though it may, under certain 
 circumstances, prove its, existence, yet, as a mea- 
 sure of its degree, must, as this candid author 
 himself acknowledges, be highly fallacious. 
 
 In order to ascertain the duration of the vital, 
 contractile power of arteries, Mr. Hunter 
 chose, for the subject of his experiment, those of 
 the umbilical cord, because, says he, “ I could 
 “ confine the blood in them, and keep them dis- 
 “ tended for any length of time. In a woman 
 “ delivered on the Thursday afternoon, the navel 
 “ string- was separated from the foetus. It was 
 “ first tied in two places, and cut between, so 
 “ that the blood contained in the cord and pla- 
 “ cenfa was confined in them. 
 
 “ The placenta came away full of blood ; and 
 “ on Friday morning, the day after, I tied a 
 “ string round the cord, about an inch below the 
 “ other ligature, that the blood might still be 
 “ confined in the placenta and remaining cord. 
 “ Having- cut off this piece, the blood immedi- 
 “ ately gushed out, and by examining the cut 
 “ ends of the cord, I attentively observed to what 
 “ degree the ends of the arteries w'ere open, and 
 
 the blood having now all escaped from this 
 “ portion, the vessels were left to contract w ith 
 
56 On the Powers of Arteries. 
 
 ‘‘the whole of their elastic power, the effect of 
 “ which is immediate. 
 
 “ Saturday morning', the day after this last 
 “ part of the experiment, having examined the 
 “ mouths of the arteries, I found them closed 
 “ up ; so that the muscular coat had contracted 
 “ in the twenty-four hours, to such a degree as 
 “ to close entirely the area of the artery. That 
 “ same morning, I repeated the experiment of 
 “ Friday ; and on Sunday morning, observed the 
 “ result of the second experiment to be similar 
 “ to that of the former. 
 
 “ On this morning, Sunday, I repeated this 
 “ experiment the third time ; and on Monday, 
 “ observed that the result had not been the same 
 “ as before, the mouths of the arteries remaining 
 “ open, which shewed that the artery was be- 
 “ come dead. 
 
 “ These experiments shew that the vessels of 
 “ the cord have the power of contraction above 
 “ two days after separation from the body.”* 
 
 In this relation there seems to be an incon- 
 gruity so great, that one wonders how it could 
 have escaped the attention of the author. How- 
 all the blood in a small artery could have imme- 
 diately escaped, except by a complete contact of 
 * Treatise on the Blood, See. p. 11(5. 
 
On the Powers of Arteries. 57 
 
 its sides from elasticity, and therefore how any 
 subsequent diminution of its area could have 
 taken place from the same, or any other power, 
 it is difficult to conceive. 
 
 Without, however, cavilling- about words, I 
 several years ago determined to examine into 
 the fact, which my situation as physician to the 
 Puerperal Charity in this city, of which the 
 Messrs. Norman are accoucheurs, and in 
 which between three and four hundred women 
 are annually delivered, gave me almost daily 
 opportunities of doing. 
 
 Accordingly a placenta and cord were ob- 
 tained, treated in the manner described by Mr. 
 Hunter. No sooner, however, was the cord 
 cut through by Mr. George Norman, than 
 the blood gushed out, and the arteries contracted 
 to an almost invisible point, evidently incapable 
 of any farther perceptible reduction of area. 
 
 Thinking, however, possible, what I am now 
 farther inclined to believe is true, that, after the 
 cessation of circulation in the cord, the arteries 
 might, by their vital power, expel part of their 
 blood into the placenta, I suggested the pro- 
 priety of making three ligatures before the 
 separation of the cord from the foetus; in con- 
 sequence of which, the blood would be more 
 
58 
 
 On the Powers of Arteries. 
 
 perfectly retained between the two which were” 
 more remote, than in the former experiment. 
 It turned out that the arteries actually ap- 
 peared more turgid with blood, though from 
 what cause I do not presume to say. The cord 
 being’ now cut through between the ligatures, 
 the blood was forcibly expelled, and the arteries 
 at once contracted just as before. 
 
 Both experiments were made at a much 
 earlier period after delivery, than that stated by 
 Mr. Hunter ; and no diminution whatever in 
 the opening of the arteries could be perceived 
 the next day. 
 
 In his experiment, one day had elapsed be- 
 tween the delivery of the placenta, and the trial 
 to which the funis w as subjected. It was, there- 
 fore, proper to conduct the experiment precisely 
 in the same manner. Accordingly, last summer, 
 the funis of a placenta, delivered by Mr. Coombs 
 at eleven o’clock on Friday morning, had two 
 ligatures firmly made on it previously to its 
 separation from the foetus. The blood being 
 thus retained, and at twelve o’clock at noon, 
 on Saturday, a new ligature being made on 
 the cord, at some distance from that which 
 remained, all the vessels appeared turgid 
 w ith blood. The placenta being then placed 
 
59 
 
 On the Powers of Arteries. 
 
 f&elow, and the cord held up in a perpendicular 
 direction, so that no blood could escape by its 
 own gravity, the cord was cut through between 
 the ligatures. The blood immediately sprang 
 out with considerable force, and even for some 
 short time continued to ooze from one of the 
 arteries, leaving the orifices of both much more 
 patulous than in the two former experiments. 
 Another ligature was made farther on, and the 
 intervening part cut through, with precisely the 
 same effects as before. All the portions thus 
 divided were put into clean water, and laid 
 aside until half-past twelve on Sunday. The 
 various sections being then examined, no differ- 
 ence in the size of any of the arterial orifices 
 from that of the preceding day could be per- 
 ceived. So far, indeed, were these arteries from 
 being fully contracted, that some of them still 
 contained blood. 
 
 The result of this experiment, therefore, dif- 
 fered from that of the two former, inasmuch as 
 the tonicity of the arteries seemed to have been 
 totally or nearly lost, previously to the several 
 sections. • 
 
 These different modes appearing too indis- 
 tinct or uncertain to lead to any decisive con- 
 clusion as to the facts which they were intended 
 
60 
 
 On the Powers of Arteries. 
 
 to ascertain, it seemed expedient to prosecute 
 the enquiry by other experiments. 
 
 In a late work, I stated the well-known fact, 
 that, in the dead body, the arteries are usually 
 found more or less deprived of their blood; and an 
 attempt was made to explain this fact, by suppo- 
 sing that, after apparent or animal death, arteries 
 were contracted by their tonicity beyond that 
 degree which would have been otherwise per- 
 mitted by their elasticity. Hence the blood 
 would be, in a certain proportion, expelled into 
 the veins ; but the tonicity soon ceasing, with the 
 other powers of organic life, the arteries would be 
 dilated by their elasticity, and would therefore 
 remain more or less robbed of their blood.* 
 
 In order to ascertain this point, the following 
 experiments were made. 
 
 The carotid artery of a living Ram having 
 been detached from all the surrounding parts, 
 its circumference was accurately measured with 
 some fine thread, and found to be lAl of an 
 inch. The animal was then killed by a cord 
 passed round the trachea, without including any 
 other part. The artery being again measured 
 precisely in the same spot, within five minutes 
 after apparent death, was found to be in cir- 
 * Elements of Pathology and Therapeutics, v. i. parag. lsiii 
 
On the Powers of Arteries. 
 
 61 
 
 cumference only 444 of an inch. Thus the cir- 
 cumference appeared to have been reduced 
 of an inch. 
 
 In order to discover whether any, and how 
 much, of this reduction depended on tonicity, 
 it was presumed that a subsequent period might 
 be found, when the tonic contraction would be 
 entirely lost, and the artery would be brought 
 to that state, which was the result of the me- 
 chanical power of elasticity. 
 
 Accordingly, twenty-one hours and a half 
 after the last measurement, putrifaction having 
 already begun about several parts below the 
 diaphragm, the artery was measured in the 
 same place a third time, and proved to be in 
 
 circumference 44-5- an inch. 
 
 Hence, of the whole contraction of the cir- 
 cumference, or of an inch, that by tonicity 
 was an inch, and that by elasticity 
 
 In another Ram, the circumference of the 
 carotid before death was of an inch. The 
 animal being killed by strangulation, as before, 
 the vessel, measured in the same spot, six minutes 
 after the first application of the ligature, w as 
 found to be in circumference only -|44- of an 
 inch. Being again measured nearly twenty- 
 * Experiment XIII. 
 
62 
 
 On the Powers of Arteries. 
 
 four hours afterwards, its circumference was 
 44.-5- Here, then, the tonicity was as an 
 
 inch, and the elasticity as 
 
 Both these animals having 1 been in a state of 
 perfect health and great vigour, when the first 
 measurements of the carotid were made, and 
 being in a state of incipient petrifaction at the 
 last measurements, we may fairly conclude the 
 first set to be indicative of the condition of the 
 several arteries during the possession of the full 
 powers of life, and the last, of the same arteries 
 during the total loss of those powers. 
 
 If it be objected to the accuracy of these 
 conclusions, that the arteries had possibly con- 
 tracted themselves previously to the first mea- 
 surements, as is well known to happen under 
 certain circumstances of exposure ; I answer, 
 that, being well aware of this effect, care was 
 taken by the experimenters to perform the mea- 
 surements in much less time than that, which 
 ample experience had shewn to be necessary for 
 that effect. 
 
 In a fat Wether, full-grown, the circumfe- 
 rence of the carotid was 244. of an inch. The 
 animal was bled to deatli by an incision in the 
 other carotid; and in fifteen minutes after this 
 * Experiment XV. 
 
On the Powers of Arteries. 63 
 
 incision, the first artery measured in circumfe- 
 rence 444 ail inch. Sixteen hours after, the 
 circumference was '44 of an inch. Here the 
 contraction by elasticity seemed to be as of 
 an inch, and that by tonicity as only ot 
 an inch.* 
 
 In this experiment, however, it is probable 
 that an insufficient allowance was made for the 
 tonicity, and too great an allowance for the 
 elasticity. In reality, one might at first view be 
 disposed to conclude, that there were some re- 
 mains of tonicity at the third measurement^ 
 since not only the interval was shorter, but the 
 abdominal viscera had been removed immedi- 
 ately after death, and the animal was hung up 
 in a cool place, for the express purpose of sup- 
 plying the table. Hence the carcase was per- 
 fectly fresh at the time of the third measurement, 
 and continued so for four days afterwards ; 
 whereas, in the two former cases, from the re- 
 tention of the blood and viscera, and exposure 
 to a greatly heated atmosphere, putrifaction, as 
 before observed, had already begun, and all 
 tonicity was of course lost. 
 
 At a still more advanced and a cooler season, 
 the right carotid of a large Horse was found to 
 * Experiment XVI. 
 
64 * 
 
 On the Po/vci's of Arteries. 
 
 be in circumference 444 of an inch. He was 
 killed by opening 1 the left carotid; and as soon 
 as he had ceased to move, the right, measured 
 in the spot before examined, was in cir- 
 cumference ±44 of an inch. The next morning 1 , 
 fifteen hours and a half after the last measure- 
 ment, the circumference was ±44 of an inch. 
 Hence, of the whole first contraction, °r 444 of 
 an inch, that by elasticity seemed to have been 
 44 I of an inch, and that by tonicity In this 
 
 experiment, as in that last mentioned, from the 
 shortness of the time, and the total want of putri- 
 faction, it is possible that the tonicity was not 
 entirely lost ; and, therefore, that too great an 
 allowance was made for the contraction of the 
 artery by elasticity.* 
 
 In a fifth case, a Ewe, the right carotid of 
 which, after a ligature on the left, was ±44 of 
 an inch round, was bled to death ; in conse- 
 quence of which, the circumference of the artery 
 was immediately diminished to ±44 °f an inch, 
 but afterwards rose to ±44 °f an ineh.f 
 
 With regard to the reasons suggested for the 
 apparent defect of tonicity in Experiments XVI. 
 and XXI. however specious they may at first 
 appear, their validity is justly rendered doubtful, 
 * Experiment XXI. f Experiment XXIV. 
 
On the Powers of Arteries. 
 
 65 
 
 by certain circumstances, which occurred in 
 Experiment XXIV. some other results of which 
 have just been detailed. 
 
 In this experiment it was found, that, at five 
 minutes after apparent death, the circumference 
 of the carotid had risen from ^44 to ±44. of an 
 inch ; and at ten minutes after death, to -ll-i of an 
 inch, which was the full dilatation which it 
 reached, even after the commencement of 
 putrifaction. 
 
 Now as in Experiment XVI. the first mea- 
 surement after apparent death is stated as having 
 been at ten minutes, it is not improbable that 
 the artery had already begun to dilate by a 
 diminution of its tonicity; and consequently, that 
 the whole sum of the tonicity is not accounted for. 
 
 A similar deficiency may have taken place in 
 Experiment XXL in which no period is assigned 
 for the first measurement after apparent death. 
 To which may be added, that, in the latter case, 
 the animal had undergone some previous expe- 
 riments, the relation of which would not be ap- 
 posite to our present purpose, but which might 
 have had some influence on the tonicity of the 
 artery during life. 
 
 Another point, also, deserves attention. It 
 appears from Experiment XXIV. that in an ani- 
 
 F 
 
66 On the Porters of Arteries. 
 
 mal, whose heart, after large blood-letting, still 
 beats, and respiration continues, the carotid may, 
 by that process, have been reduced to the utmost 
 degree of which it is capable, after those func- 
 tions have entirely ceased. Since also, as far 
 as that experiment goes, it appears that the 
 tonicity of an animal bled to death is very quickly 
 evanescent, and since the instances of apparent 
 defect of tonicity, which I have adduced in 
 Experiments XVI, , and XXI. were only those 
 of animals killed by bleeding ; it may be con- 
 jectured, that the dilatation by elasticity had in 
 these cases already begun to take place, and, 
 therefore, that the maximum of contraction had 
 elapsed, and was not fully measured. 
 
 This conclusion receives great additional force 
 from what occurred in Experiment XXVII., in 
 which, after the loss of forty-one ounces of blood, 
 the circumference of the carotid of a Ewe was 
 reduced to the utmost degree that it could reach 
 by apparent death : Subsequently to which 
 
 period, although the ewe was still alive, the 
 artery, after the farther loss of eight ounces of 
 blood, dilated of an inch ; and after the 
 additional loss of ten ounces, which finally killed 
 the animal, the dilatation was immediately in- 
 creased T 4-r of an inch. Eighteen minutes af- 
 
On the Powers of Arteries. 67 
 
 terwards, the circumference rose i nine 
 minutes more and in six minutes more 
 Hence, it appears, that while, after large eva- 
 cuation of blood, life remains, the tonicity of an 
 artery may have entirely lost its preponderance 
 over the elastic power, although some time may 
 still elapse before the ultimate effect of the latter 
 shall have taken place. 
 
 In most of these cases, the changes produced 
 on the size of the arteries, at the different stages 
 of the experiments, were so great, as to be imme- 
 diately perceptible, on the slightest examination. 
 Neither were they confined to the carotids only; 
 for in the femoral of a sheep, and in the aortee 
 of rabbits, they were sufficiently conspicuous, 
 although their degree was not ascertained by 
 actual admeasurement.* The general result 
 corresponds with those related above with regard 
 to the umbilical cord ; in which the contraction 
 of the arteries was entire after a short period, but 
 ceased at the end of twenty-four hours. 
 
 Whether the difference observed in the funis 
 in Mr. Hunter’s experiment depended on the 
 season, the desiccation of the arteries, or any 
 other assignable cause, his narration does not 
 enable us to judge. 
 
 * Experiments XI. XII. XIII. XIV. XXV. 
 
 F 2 
 
G8 On the Powers of Arteries. 
 
 It is, indeed, probable, that the proportion 
 between the tonic and elastic powers may greatly 
 vary, not only in different arteries, and in diffe- 
 rent animals, but in the same individual animal 
 at different times. So also the distention of an 
 artery by its contained blood may vary, with the 
 same modifications as those just expressed; so 
 that any single experiment, such as I have de- 
 scribed, can only be considered as relative to 
 those circumstances. 
 
 In the mean while, the general principle of 
 the existence of two moving powers in arteries 
 of warm-blooded animals is, by these experi- 
 ments, illustrated; and the theory of the cause of 
 the greater or less bloodlessness of the lancer 
 arteries after death, advanced in the work, to 
 which I have alluded, is fully established. 
 
 The facts, which I have adduced, lead to con- 
 clusions as to the usual state, and relative pro- 
 portions, of the moving powers of arteries, very 
 different from those of preceding physiologists, 
 and more especially Mr. Hunter. That writer 
 considers “ the natural pervious state of an 
 “ artery, to be that to which the elastic power 
 “ naturally brings a vessel, which has been 
 “ stretched beyond, or contracted within, the 
 “ extent which it held in a state of rest. The 
 
On the Powers of Arteries. 69 
 
 ** stretched is that state produced by the impulse 
 “ of the blood in consequence of the contraction 
 “ of the heart ; from which it is again brought 
 “ back to the natural state by the elastic power, 
 “ perhaps assisted by the muscular.”* From 
 this, and several succeeding passages in the same 
 work, it appears to have been the opinion of Mr. 
 Hunter, that the natural state of an artery 
 during life is that, to which the elastic power 
 spontaneously brings it, when no longer forcibly 
 distended by the systole of the heart ; that is, 
 during the diastole of that organ. 
 
 The question, whether any such difference 
 from the systole and diastole of the left ventricle, 
 as is assumed by Mr. Hunter, usually obtains, 
 in a living artery, will be a subject of subsequent 
 inquiry. In the mean while, the experiments, 
 which I have related, demonstrate, on the con- 
 trary, that, during health, the larger arteries of 
 a living animal, as well under the diastole as 
 systole of the left ventricle, are in a state of 
 distention, to which they are forcibly impelled 
 by their contained blood, against their mecha- 
 nical power of elasticity. This was in fact the 
 case in the experiment of the arteries of the um- 
 bilical cord, described by Mr. Hunter himself; 
 
 * Hunter on the Blood, See. p. 11(3. 
 
70 On the Powers of Arteries. 
 
 who admits, that, the sudden expulsion of the 
 blood, when the cord was divided between two 
 ligatures, was the result of the operation of the 
 elastic power, acting immediately on the con- 
 tained blood, as soon as the obstacle to its action 
 was removed. 
 
 In order farther to enquire into this point, two 
 ligatures, distant from each other an inch and a 
 half, were at the same instant tightly drawn on 
 the carotid of a living sheep. This artery, mea- 
 sured half way between the ligatures, was found 
 to be in circumference £4-§- of an inch. The 
 blood being suffered to flow out of this included 
 part, by means of a puncture with a lancet, the 
 artery in the same spot as before, measured in 
 circumference only of an inch. Hence the 
 circumference appeared to have been immedi- 
 ately reduced -A4 of an inch, by the mere eva- 
 cuation of the blood contained in the artery.* 
 
 In a Horse, the right carotid artery was in 
 circumference ^44 of an inch. After a short 
 time had been occupied in examining its move- 
 ments, it was firmly tied at some distance before 
 the part measured. Some farther observations 
 having been made, a second ligature was applied 
 an inch beyond the first ; and, in an hour after- 
 * Experiment XVI. 
 
On the Powers of Arteries. 71 
 
 wards, care being taken to avoid the point mea- 
 sured, the portion between the ligatures was 
 punctured. Little more than serum flowed out; 
 the blood, as appeared from subsequent exami- 
 nation, having coagulated in the artery. The 
 vessel being now measured in the same part as 
 before, was found to be in circumference only 
 444 of an inch. The next morning, sixteen 
 hours and a quarter after the animal had been 
 killed, by bleeding from the left carotid, the cir- 
 cumference of the artery, at the same point, was 
 441 of an inch. Hence the elasticity was as 
 414 of the circumference of the artery, and the 
 tonicity as 44L* 
 
 From these two last experiments, it appears, 
 that the forced distention of the artery does not 
 necessarily depend on the impulse of the blood 
 from the systole of the ventricle, since it existed 
 when the communication with the stream of 
 blood from the heart was interrupted by a 
 ligature. 
 
 As, during the common circumstances of 
 health, arteries are naturally distended beyond 
 that degree, to which they would spontaneously 
 contract by their elastic power, so they are 
 capable of suffering a still greater degree of 
 * Experiment XX. 
 
72 
 
 On the Powers of Arteries. 
 
 distention, from increased fulness of blood in the 
 general system, or from those excessive determi- 
 nations of blood to particular parts which occur, 
 on various occasions, in the animal frame. Thus 
 it is generally admitted, that, if the passage of 
 the blood through one arterial trunk is inter- 
 cepted, the collateral branches, supplying- the 
 part, undergo an increased distention, in order 
 fully or partly to compensate the loss. 
 
 This conclusion was rendered very probable 
 by what occurred in the Ram, Experiment XV. ; 
 in which one carotid had been tied nearly eleven 
 months before, and the other was found much 
 larger than any that we had before observed. 
 
 In order, however, more accurately to investi- 
 gate this point, the right carotid of a small 
 Ewe having been found to be in circumference 
 of an inch, the left carotid w as tied ; a 
 few minutes after which, the right had gained 
 in circumference °* an inch.* 
 
 In another Ewe, the right carotid, being 
 of an inch in circumference, was again measured 
 twelve minutes after the left had been tied, and 
 was found to have gained in circumference T VL- 
 of an inch.f 
 
 * Experiment XXIII. 
 
 t Experiment XXIV. 
 
On the Powers of Arteries. 
 
 73 
 
 I know of no actual measurements to prove 
 that a similar effect takes place, in inflammation 
 and other maladies, in the larg'er arteries sup- 
 plying- the parts so affected ; but we may rea- 
 sonably presume its existence from the tangible, 
 and sometimes visible, increase of size in the 
 artery, as well as from the great perceptible 
 enlargement of the veins leading from the dis- 
 eased parts. 
 
 From various preceding considerations, it is 
 natural d priori to conclude, that when, under 
 the state not only of the usual healthy dilatation 
 of arteries, but of that increased dilatation 
 which often accompanies disease, the distending 
 cause, which is a certain quantity or momentum 
 of blood, is diminished, the elasticity will tend 
 to contract them, so as, within certain limits, to 
 accommodate them to the quantity of blood 
 which they ought to convey. If, however, the 
 elasticity alone should be inadequate to the 
 requisite force or degree of contraction, the to- 
 nicity, or vital power, may assume the office of 
 contraction, where it was left by the elasticity, 
 and carry it to the necessary extent. 
 
 In order to ascertain how far this accommo- 
 dation of arteries to the loss of blood from the 
 system would reach, I suggested the Experiment 
 
74 
 
 On the Powers of Arteries. 
 
 XXIV. ; in which, the circumference of the 
 right carotid in a Ewe having been first raised, 
 by a ligature on the left, from 444 of an inch 
 to 444> was successively diminished to 444> 
 
 *5* 135 2 3 5 2 2 2 201 191 I6l £ * ..X K,_ 
 
 400) 4uo» 4^ 4out snci too 01 311 men, oy 
 
 as many blood-lettings of eight ounces each, 
 from the left jugular vein, till the death of 
 the animal. 
 
 So, also, in Experiment XXVII., the right 
 carotid of another Ewe, which was 444 of an 
 inch in circumference, was successively reduced 
 to *§4> vo!> i4§> 4ol, and ill of an inch, by si- 
 milar bleedings from the same vein. 
 
 Hence we may understand, how readily the 
 arteries may become more or less capacious, in 
 proportion to the quantities of blood which may 
 either exist in the whole system, or may be de- 
 termined to particular parts. 
 
 It is, however, probable, that the relative 
 capacities of entire arteries, or of certain parts 
 of them, may be affected by other agents, besides 
 the mere immediate quantity of blood which 
 they contain. This evidently happens under 
 certain circumstances of the exposure of arteries 
 in living animals. Thus, in Experiment XIII., 
 a very narrow ring of a carotid became, while 
 it was under examination, contracted, as if a 
 
7.3 
 
 On the Powers of Arteries. 
 
 small ligature had been half tightened around 
 it. So, also, in Experiment XXIV., a portion 
 of the left carotid of a Ewe, which was ■!-§.*- of 
 an inch in circumference, after having been half 
 an hour denuded, was found to be only -1 44 of 
 an inch ; while at the same time the continuous 
 portions before and beyond, which had been 
 more recently laid bare, appeared, even to the 
 eye, to be proportionably augmented. One of 
 these portions, which was beyond the contracted 
 part, was measured, and found to be 44-4 of an 
 inch in circumference, or to have gained ; 
 but while we were preparing to measure the 
 other dilated portion, we saw it shrink to nearly 
 the same size as the contracted part. Again, in 
 Experiment XXVII. there was a considerable 
 smallness of one portion of the artery, relatively 
 to the adjacent parts before and beyond. 
 
 It is worthy of being remarked, that this 
 partial reduction of circumference was found 
 in the progress of the last experiment but one, 
 to be the utmost extent which it was capable of 
 reaching, from the want of the distending power 
 of the blood within the artery. 
 
 In another instance, the different changes 
 from dilatation to contraction, and the contrary, 
 arising under exposure, were more sudden than 
 
76 
 
 On the Powers of Arteries. 
 
 any which we had before witnessed. In th<?~ 
 same experiment, there was an increase of size 
 in one carotid from a ligature on the other, and 
 a spontaneous enlargement of the artery before 
 the contracted part, just as had been observed 
 in Experiment XXIY. In the present instance, 
 that enlargement was capable of being tolerably 
 well ascertained by measurement ; and was found 
 to be YeV of an inch.* 
 
 To -what immediate cause these sudden 
 changes under exposure are owing, I am unable 
 to suggest. In my experiments they occurred 
 almost wholly in Ewes, and in a few cases only of 
 these. I know not whether this was in any way 
 connected with the colder season, at which 
 the experiments, exhibiting those phenomena, 
 were made. That the contraction is not owing 
 to mere cold, is at first sight probable ; since^ 
 in one experiment, a long-continued application 
 of ice to the denuded carotid of a ram, had no 
 effect whatever of this kind. This fact, how- 
 ever, affords only some degree of probability ; 
 for the difference may have originated in a less 
 degree of excitability in the living arterial coat 
 of the male, which was exposed to this trial, 
 than in that of the female. 
 
 * Experiment XXVI. 
 
On the Powers of Arteries. 77 
 
 These contractions were, however, much too 
 sudden and apparent, to vitiate any of the con- 
 clusions deduced from the foregoing experiments, 
 relatively to the changes produced on arteries, 
 either by death, or by the evacuation of blood 
 from the system or the part. 
 
 Neither could they, as it should seem, be in 
 any way attributable to the mechanical power of 
 elasticity ; since they occurred in the most rapid 
 manner, not only from enlargement to contrac- 
 tion, but the reverse, alike under similar states 
 of desiccation, under the putrifaction and actual 
 life of other parts of the system, and at the same 
 time respectively in different parts of the same 
 artery, exposed to the same causes of mecha- 
 nical dilatation. 
 
 As, in all these experiments, no evidence 
 exists, that the living fibres of the middle coat of 
 arteries have, like the radiated fibres of the iris, 
 any inherent power of elongation, from the ap- 
 plication of any known stimulus ; but, it appears, 
 on the contrary, that their action is that of short- 
 ening or contraction, we are, so far, obliged to 
 conclude, that, in the dilatation of an artery, these 
 fibres are altogether passive. Hence it follows, 
 that they are no farther concerned in that dilata- 
 tion, than as, through defect of tonic exertion, they 
 
78 On the Powers of Arteries. 
 
 may yield to causes of distention, from within 
 or without. 
 
 So, also, with regard to the elasticity ; it is 
 obvious, that, as arteries are already dilated 
 beyond the degree, which that agent, if not 
 counteracted, would have permitted, any in- 
 crease of dilatation must arise, not from an 
 augmentation, but a diminution, of the action 
 of that power. Hence, the dilatation, so far 
 as respects elasticity alone, will be in the 
 compound ratio of the momentum of blood in 
 the vessel, and the want of resistance in its 
 coats ; so that, the contractile power of the 
 coats being given, the dilatation will be directly 
 as the momentum of blood in the vessel ; and, 
 on the other hand, the momentum being given, 
 the dilatation will be inversely as the con- 
 tractile power of the coats. 
 
 From these two positions taken in connection, 
 we are, without any danger of refutation from 
 the preceding experiments, compelled to admit 
 as the cause of the common dilatation of the 
 larger arteries, and still more forcibly of that 
 which is preternatural, the mechanical distend- 
 ing power of the blood which they contain. 
 
 Hence it probably follows, not only that one 
 carotid is dilated on the tying of the other, by 
 
On the Powers of Arteries. 79 
 
 the mere mechanical impulse of a larger quan- 
 tity of blood than it had usually received, but 
 that, in the instance adduced of an unusual dila- 
 tation of an artery immediately before a portion, 
 which was preternatiu ally contracted, and, in 
 another instance, both before and beyond it, 
 that dilatation was owing to an accumulation of 
 blood, in some mode dependant on the neigh- 
 bouring contraction. 
 
 This increase of diameter in adjoining por- 
 tions of the same vessel does not, however, 
 always occur, when the perviousness of the artery 
 is completely destroyed by a ligature. Thus, in 
 Experiment XXIII., the circumference of the 
 right carotid, which was 444 of atl inch, and 
 which was increased to 444 by a ligature on the 
 left, was reduced to its former dimensions by 
 a ligature on the former beyond the measured 
 part. The left carotid, also, which had been first 
 tied, and had appeared to be nearly of the same 
 size as the right, was now so shrunk before the 
 ligature, as to be in circumference only 444 °f 
 an inch. 
 
 From the various results which have been 
 described, we are obliged to attribute to the 
 larger arteries a much greater force and sum of 
 tonicity than are admitted by Hunter and 
 
80 
 
 On the Powers of Arteries. 
 
 A 
 
 Bichat ; who contend that, in this series, they 
 exist in a very small degree. 
 
 In the first place, with regard to force, we 
 have seen that it is capable of completely over- 
 coming that elasticity, by which an artery is 
 spontaneously dilated to a mean degree, but 
 which ineffectually acts, until the tonicity is lost 
 by the perfect death of the part. 
 
 Next, with regard to the sum or quantity of 
 tonicity ; it has been shewn that the degree im- 
 mediately exhibited on the first abstraction cf 
 the blood, which counteracts the contraction of 
 the artery, is nearly equal to the sum of the elas- 
 ticity. If to this, also, we add the tonic power, 
 by which, during life, an artery is farther ca- 
 pable of being contracted to a mere impervious 
 cord, it must be admitted, that the tonicity 
 greatly exceeds the elasticity. 
 
 All the conclusions, which have thus been 
 formed as to the powers of arteries, are derived 
 from observations made on the carotids only ; 
 but if we assent to those of Mr. Hunter re- 
 specting the increase of tonicity proportionably 
 to the diminution of diameter, the carotids in 
 sheep will possess a low degree of this faculty. 
 With some allowance, therefore, as to the relative 
 sum of the elastic and tonic powers, the same 
 
On the Powers of Arteries. 81 
 
 general principles may, doubtless, be extended to 
 all ; since the largest arteries have a considerable 
 degree of tonicity, and the smallest, as Mr. 
 Hunter very properly observes, must have 
 elasticity enough to maintain them in a state, 
 sufficiently pervious to admit of the passage of 
 blood through their cavities. 
 
 It is probable, that Mr. Hunter’s conclusion, 
 with regard to the proportion of tonicity, res- 
 pects the relative magnitude of vessels in the 
 same individual animal, and not in different 
 animals. Observation, however, has shewn me, 
 that the aorta itself, both in the abdomen and 
 thorax of rabbits, is capable of great visible 
 reduction of diameter by death ; although, on 
 account of the smallness of those animals, these 
 arteries in them appeared to be unfit objects, on 
 which to attempt a measurement of the actual 
 proportions of elasticity and tonicity. It is, 
 also certain, that in the human aorta, several 
 hours after death, a great diminution of the usual 
 quantity of blood is often observable ; whence, 
 on the principles already laid down, we may 
 infer, that this artery is possessed of a conside- 
 rable degree of tonic power. The human aorta, 
 also, like arteries of a smaller size, has been 
 
82 On the Powers of Arteries. 
 
 found in a state of complete coalescence and 
 imperviousness. 
 
 The facts, which have been related, afford a 
 probable reason why, in the experiments of 
 Haller, the circulation of the blood proceeded, 
 for a certain time, in microscopic arteries, after 
 ligatures on the aorta, or even the entire separa- 
 tion of that artery from the heart. The larger 
 arteries continuing to contract by their tonicity, 
 the blood, during that period, must necessarily 
 have gone on suffering slow propulsion from them 
 into the smaller or capillary branches of the 
 same system, and through that into the veins. 
 
 It is, probably, from the same cause, that, in 
 the experiments of Haller and Spallanzani, 
 not only a puncture in any part of an artery, in 
 which the circulation had become either lan- 
 guid, or even had for a short time wholly ceased, 
 occasioned an increase or renewal of circulation; 
 but the blood in adjacent portions of the same 
 vessel, or in neighbouring vessels, flowed towards 
 the puncture, sometimes in a retrograde direc- 
 tion, and at other times against its own gravity. 
 For, if the whole arterial system, stretched be- 
 yond what may be termed its natural degree, 
 were spontaneously tending towards contraction 
 by its elasticity or tonicity, or both, and the 
 
On the Powers of Arteries . 
 
 83 
 
 resistance to this contraction were any where 
 diminished by a puncture, it is evident, that to 
 that point the blood, if fluid, would be compelled 
 to flow from within a certain distance ail around 
 the punctured part. 
 
 Although, however, this contraction of vessels 
 is the probable cause of the phoenomena just 
 described, to which Haller gives the name 
 of “ Derivation I am far from asserting, that it 
 is the cause of all the motions of the blood ob- 
 servable in arteries, after the influence of the 
 heart on it has been destroyed. The experi- 
 ments of Haller abundantly prove, that irre- 
 gular movements of this kind may occur from 
 mechanical agitation, from gravitation, from 
 the attraction between the coats of the vessels 
 and the globules of blood, and probably of these 
 globules towards each other. All these move- 
 ments are, however, most essentially different 
 from that which arises either from the systole of 
 the left ventricle of the heart, or from the gradual 
 contraction of vessels by their own inherent 
 powers, after the cause of distention has been 
 wholly, or in part, removed.* 
 
 * See Haller; Memoire sur le Mouvement du Sang, I. chap- 
 v. vi. Memoire II. p. 338 to 341. edit. Lausanne. Ano- 
 ther cause of these movements has also suggested itself to 
 me; but I have not had time to inquire into the fact by- 
 actual experiment. 
 
 G 2 
 
84 On the Powers of Arteries. 
 
 The existence of such a process, in certain 
 animals of warm blood, has been sufficiently 
 proved by the preceding’ experiments. Hauler, 
 indeed, asserts, that, in the arteries of certain 
 cold-blooded animals, as frogs and toads, he 
 could perceive no constriction whatever. To 
 me, however, it seems, that to this opinion there 
 are several powerful objections. For, first, his 
 conclusion on this subject is partly theoretical; 
 being apparently founded on the fact, that, in 
 these animals, the systole of the heart produces 
 no more dilatation of the arteries, than if they had 
 been tubes of glass ; whence he infers, that, 
 where there is no dilatation, there can be no 
 contraction. In this reasoning, therefore, like 
 other writers, he confounds the occasional tonic 
 contraction, with a supposed uniform contraction 
 during the diastole of the ventricle. 
 
 He, however, speaks of the want of con- 
 traction, as a matter of actual observation. But 
 even this circumstance is by no means conclu- 
 sive, since, in the first place, his observations are, 
 for the most part, made on microscopic arteries, 
 too small to admit of any mode of measure- 
 ment; and, secondly, these amphibia are so 
 tenacious of life, that the arteries themselves, 
 although of a larger size, might not have reached 
 
On the Powers of Arteries. 85 
 
 that degree of contraction, which could be per- 
 ceived by the eye, although it might be suffi- 
 cient, by slow gTadation, to carry on the blood, 
 and to determine it to any aperture in the vessel. 
 So little, indeed, does Haller himself rely on 
 his own observation, as to the want of contraction 
 in the arteries of these amphibia, that he doubts 
 w’hether the phenomena of derivation may not 
 depend on “ une contraction invisible et innee 
 l( des parois des vaisseaux.”* 
 
 In his large work on Physiology, referring to 
 that just quoted, he again assigns this movement 
 of the blood after death, or after the exclusion 
 of the arterial system from the agency of the 
 heart, to a contraction, which depends neither 
 on life, nor on any muscular power, but on the 
 native elasticity of the cellular coat. “ Nunc 
 “ sincerus aliud phenomenon propono, quod non 
 “ videtur absque aliqua contractione intelligi 
 “ posse. Ea vero contractio a vita non pendet, 
 “ neque musculosse est indolis, quee a morte 
 “ supersit, et ad nativum potius elaterem tensce 
 “ fibre cellulose spectat. Ea enim alio etiam 
 “ in exemplo, sedlente, etmultis continuis diebus 
 “ arterias calidorum animaliumresectasexinanit, 
 * Ibid. p. 162, )63. 
 
86 
 
 On the Powers of Arteries. 
 
 “ diametruinque minuit, et lumen delet.”* For 
 the evidences of the truth of this opinion, he 
 refers to vol. i. page 72. Had this illustrious 
 author been acquainted with the more recent 
 discoveries as to the living power of arteries, he 
 would not have attributed to elasticity alone the 
 facts which he relates. 
 
 Spallanzani admits of two instances, in 
 his experiments, of a considerable reduction of 
 diameter, from depletion, in the descending- 
 aorta ; but of what animals he does not inform 
 us. It is probable, that he alludes to salaman- 
 ders and green frogs, (“rainesvertes,”) though 
 he denies any such reduction in various other 
 experiments, f 
 
 He, however, falls into an error similar to 
 that of Haller ; inferring, that the strongest 
 support of the truth of that physiologist’s opinion 
 of an actual contraction in these vessels would 
 be the discovery of their power of dilatation ; 
 with regard to which, however, his experimen- 
 tal results were different on different occasions.! 
 
 I greatly regret, that various circumstances, 
 attendant on the advance of the season, have 
 
 * Physiologia, lib. vi. sect. i. §. xi. 
 t Experiences sur la Circulation, &c. Diss. III. Exp. 1 3(5, 138. 
 
 J Ibid. p. 383. 
 
On the Powers of Arteries. 
 
 87 
 
 obliged me to postpone any experimental inqui- 
 ries into the nature and order of the phenomena 
 of arteries, in the class of animals with cold blood. 
 
 Arteries, during life and health, are in a 
 forced state, not only of lateral distention, but 
 also of elongation. Hence, when they are any 
 where divided, the cut ends suffer a considerable 
 degree of retraction. In a Ewe, two ligatures 
 on a carotid, having been made exactly one inch 
 distant from each other, and the artery having 
 been divided in the middle between them, the 
 distance between the ligatures immediately be- 
 came | 44 - °f an inch ; so that the retraction was 
 full one fourth of the length of the artery inclu- 
 ded between the two ligatures.* 
 
 Since, however, in this experiment, the in- 
 crease of distance between the ligatures, on the 
 division of the artery, was, perhaps, the sum of 
 the w ? hole contraction on each side, from the 
 divided part to the remotest attachments of the 
 vessel, I endeavoured to obtain a more correct 
 result in the following way. Two ligatures, 
 distant from each other 444. °f an inch, were 
 made on the carotid of a living Ewe. A third 
 ligature was now made beyond the second ; and 
 between these two the artery was divided. 
 
 * Experiment XXII. 
 
88 On the Powers of Arteries. 
 
 Nothing then existing to counteract the con- 
 traction of every portion of the artery, the 
 distance between the first and second ligatures 
 was again measured, and found to be 444- of an 
 inch. Whence it appears that the retraction of 
 this portion was or somewhat less than f .f 
 It is probable, however, that, in this experiment, 
 the proportion of retraction is over-rated ; not 
 only because the blood in the part measured had 
 been previously evacuated, but because the agi- 
 tation of the parts from respiration, Sec. made it 
 very difficult to keep the artery in a strait posi- 
 tion, after it had been divided. 
 
 In both of these experiments, care was taken 
 to preserve the head in a similar and easy 
 position. 
 
 That power of dilatation and contraction in 
 arteries, which the foregoing experiments have 
 proved, not only to exist, but to be owing to a 
 cause partly mechanical and partly vital, leads 
 to the consideration of the nature and cause of 
 the Pulse in this order of vessels. 
 
 f Experiment XXVII. 
 
C 89 ] 
 
 THE NATURE AND CAUSE OF THE 
 ARTERIAL PULSE. 
 
 THE cause of the Pulse in the Arteries is a 
 subject so interesting 1 , that, from a very early 
 period, it has occupied the attention of physio- 
 logists. With regard to this point, they are, 
 however, still at variance. 
 
 Haller plainly considers this phsenomenon 
 as owing to the alternate dilatation and con- 
 traction of the artery from the impulse, and 
 comparative retardation, of the ware of blood, 
 corresponding with the systole and diastole of the 
 left ventricle of the heart. Thus, in his Element a 
 Physiologiae ; “ Mihi quidem de phaeno neno 
 
 “ ipso dubium nullum superest. Etsi enim 
 “ utique non rarum est in vivo animaie inciso 
 
90 
 
 The Nature and Cause oj the 
 
 “ pulsum nullum apparere, neque videri arterias 
 “ dilatari, tamen frequentes satis observationes 
 “ sunt, utique dilatationem et oculis et tangenti 
 “ diofito fuisse manifestam, ut arteriae arcum 
 “ majorem describant dum dilatantur.”* Again, 
 “ Heec alterna arteriarum micatio est quam 
 “ medici pulsum vocarunt ; quo nomine dila- 
 “ tatio quidem arteriae potissimumintelligitur.”| 
 So also, in his Memoires sur le Mouvement du 
 Sang ; “ D’abord je me suis assure que le sang, 
 “ pouss6 par le coeur, dilate les arteres, et forme 
 “ ce battement, qu’ on appelle le pouls.”J 
 In the first of these quotations, he acknow- 
 ledges, that, even in living animals examined by- 
 dissection, no pulse, or any dilatation of the 
 artery, is frequently to be seen ; but adds, that, 
 in many other instances, which he particularizes 
 in both the works which I have quoted, the di- 
 latation is sufficiently perceptible both by the 
 eye and finger. Afterwards, § in referring to 
 the parts in which the dilatation is most evi- 
 dent, he seems, with less than his usual accuracy', 
 to place the visible dilatation of the artery out 
 of the question, and only infers dilatation from 
 the sensation “ digititangentis.” This distinction 
 1 Lib. vi. sect. II. §. 9 . f Ibid. §.10. J Page 33. 
 
 § Physiologia, lib. vi. sect. II. §. 12. 
 
Arterial Pulse. 
 
 91 
 
 is of great consequence ; because, although it 
 be admitted, that the pulsation of the artery can 
 in various parts of the living body be felt, it is a 
 petitio principii to infer that it is felt because the 
 artery is dilaled. 
 
 Long after that period, Bichat, sufficiently 
 accustomed to experiments on living animals, 
 finding by the clearest evidence of sight, that, 
 in arteries denuded, there was no adequate dila- 
 tation during the systole of the left ventricle, 
 abandoned, though with apparent hesitation, that 
 opinion ; and considered the pulse as chiefly 
 owing to a locomotion, or change of place, in 
 the whole artery ; in consequence of which, it 
 springs against the finger during’ the systole, 
 and returns during the diastole. “ II me reste 
 “ a examiner comment le cceur produit le pouls 
 “ par ce mouvement brusque et instantane. 
 “ Or, nous avons encore sur ce point beaucoup 
 “ d’obscurit6 £t eclaircir ; mais on ne sauroit 
 “ disconvenir que la locomotion du systeme 
 “ arteriel ne soit pour beaucoup dans ce pheno- 
 “ m&ne. A l’instant ou la masse sanguine est 
 “ poussee ainsi du cceur vers les extremites par 
 “ un mouvement de totalite” (the simultaneous 
 movement of a continuous column) “ elle tend 
 “ inevitablement a redresser les art^res, surtout 
 
92 The Nature and Cause of the 
 
 “ quand elles sont flexueuses. Ce redressement 
 “ y determine necessairement une locomotion, 
 “ laquelle produit le battement de 1’ art&re. 
 “ Quant a la dilatation, elle est presque nulle 
 “ dans 1’ etat ordinaire.”* He adds, that if you 
 rest a little on the artery, the blood makes an 
 effort to dilate it ; and this effect increases the 
 sensation of pulse. Jadelot indeed, believed, 
 that it wholly proceeded from the latter cause. 
 
 Whatever reasons Jadelot might have 
 given for this opinion, it seems they were little 
 satisfactory to Bichat, who afterwards thus 
 concludes. “ La dilatation et le reserrement 
 “ des art^res etant peu de chose, et meme pres- 
 “ que nuls dans 1’ etat ordinaire, il paroit que la 
 “ cause speciale du pouls est dans la locomo- 
 “ tion des arteres ; locomotion qui est generate 
 “ et instantanee pour toutleur systeme.”f 
 
 In order to illustrate the term locomotion, 
 let us suppose a piece of flexible cane, which we 
 may move up and down in the direction of its 
 length, may cause to advance or recede, may 
 bend in various ways, or may even turn on its 
 own axis. These are all examples of locomo- 
 tion or change of place in the whole or certain 
 * Anatomie generate ; tom. ii, p. 335, 336. 
 f Ibid. tom. ii. p. 338. 
 
Arterial Pulse. 
 
 93 
 
 parts of the cane ; while, at the same time, its 
 diameter, or size, is in no respect changed. In 
 reality, the meaning of this term is so cleai', that 
 I should have conceived it to require no ex- 
 planation whatever, had I not actually found 
 certain persons, who could not readily distinguish 
 such movements from those of dilatation and 
 contraction, or an alternate change of diameter 
 in an artery. 
 
 The dependance of the pulse on the alternate 
 contraction and dilatation of the artery is main- 
 tained by Dumas. “ La propriety generale de 
 “ ces vaisseaux d’etre alternativement contractes 
 * ( et dilates, constitue ce que les medecins ap- 
 “ pellent le pouls.”* This dilatation and con- 
 traction he supposes, after Galen, to be inhe- 
 rent in arteries themselves, and not to depend on 
 the mechanical impulse of blood from the heart; 
 so that arteries do not dilate, because blood is 
 impelled into them ; but the blood enters them, 
 because, by their dilatation, they are disposed to 
 receive it. “ Pour se convaincre pleinement que 
 “ les art&res se contractent et se dilatent, en 
 “ vertu d’une propriety inherente a leurs parois, 
 “ il n’y auroit qu’ & r^flechir sur le but, cu la fin 
 “ de cette double action. Car puisq’ elles 
 * Principes dc Physiologie ; tom, iii. d. 314. 
 
94 
 
 The Nature and Cause of the 
 
 “ doivent recevoir et pousser le sang, elles se 
 “ disposent a la reception de ce fluide par le 
 “ mouvenient qui les dilate et Its ouvre. Elies 
 “ le chassent ensuite par celui qui les contracte 
 “ et les referme. Des-lors elles agissent avant 
 “ que le sang entre dans leurs cavites ; elles s’y 
 “ pretent d’elles-memej et ce n’ est point, coniine 
 “ disait Galien, parceque le sang y penetre qu’ 
 “ elles sont dilatees, mais plutot le sang y penetre, 
 “ parcequ’ elles se dilatent.”* 
 
 He acknowledges, however, that there is great 
 difficulty in proving this dilatation by experi- 
 ment ; but asserts that there are some parts of 
 the arterial system, in which it can easily be 
 seen; as in the arch of the aorta, and in the ca- 
 rotids, which he says evidently dilate themselves, 
 when they receive the blood from the heart. 
 “ II est assez difficile de constater la dilatation 
 “ par experience. Cependant il y ades portions 
 “ du systeme arteriel, ou les yeux peuvent 
 il aisement la saisir, comme la crosse de 1’ aorte, 
 
 * Ibid. p. 305, 306. A curious specimen of physiological 
 reasoning ! “ Arteries dilate and contract by their own 
 “ powers, because, in order to receive and expel the blood, 
 “ they must dilate and contradt by their own powers.” By- 
 similar logic, we might demonstrate life in the leather pipe 
 of a fire-engine. 
 
Arterial Pulse. 
 
 95 
 
 *« les carotides, par exemple, qui se dilatent 
 “ evidemment lorsqu’ elles re^oivent le sang 
 “ du coeur.”* 
 
 Conformably to the views of the greater 
 number of preceding physiologists, Richerand 
 also attributes the pulse chiefly tu an increase of 
 diameter in an artery, from the impulse of blood 
 by the systole of the left ventricle. “ Comrae 
 “ les art&res sont toujours pleines durant la vie, 
 “ et que le sang y coule avec d’autant moins de 
 “ rapidit6, qu’ elles sont plus eloignees du coeur, 
 “ la portion de ce fluide, que les contractions du 
 “ ventricule gauche poussent dans 1’ aorte, ren- 
 “ contrant les colonnes antecedentes, leur com- 
 “ munique 1* impulsion qu’ il a reque ; mais, 
 “ retarde, dans sa marche directe, par la resis- 
 “ tance qu’ elles lui opposent, il agit contre les 
 “ parois des vaisseaux, et les ecarte de leur axe. 
 “ Cette action laterale, par laquelle les arteres 
 “ sont dilutees, depend dont de ce que leurs 
 “ cavites sont toujours remplies par un fluide 
 <s qui r^siste k celui que le coeur y projette. 
 “ Plus considerable dans les grandes arteres que 
 “ dans celles d’ un moindre calibre, cette dilata- 
 tc tion se manifeste par un battement connu sous 
 “ le nom de pouls.”f 
 
 * Ibid. p. 314, 315. f Physiologic, torn. i. p, 319, 320. 
 
96 The Nature and Cause of the 
 
 The two last-mentioned authors speak also of 
 the advance of the artery during- the systole of 
 the ventricle, as forming part of the pheno- 
 menon of the pulse. 
 
 Portal admits of the same coincidence. 
 “ On croit generalement quele pouls est 1’ effet de 
 “ la dilatation de 1’ art&re, dependant de 1’ influx 
 “ du sang en elle ; cependant quelques physiolo- 
 “ gistes ont cru que le mouvement de loco- 
 “ motion se faisoit aussi ressentir.”* 
 
 Soemmerring contends for a similar ex- 
 planation of the pulse. “ In corpore vivo arteriae 
 “ — alio tempore magis, alio minus turgent. 
 “ Ubi nimirum arteriae sanguini, qui a vi cordis 
 “ undatim intropellitur, et illarum premit pari- 
 “ etes, cedunt, supra medium diametrum ma- 
 “ nifesto in longum et transversum extenduntur : 
 “ hie proximo temporis momento vis cordis 
 “ remittitur, arteria turn in longitudinem, turn, 
 “ et apertius quidem, in transversum, partim vi 
 “ sua elastica, partim propria vi vitali contrahitur; 
 “ et infra mediam diametrum, protrudit, deinde 
 “ denuo relaxatur, et novae sanguinis undae locum 
 “ concedit. Praeter has in arteriis magnis 
 “ tactui et quandoque visui obvias mutationes 
 “ in partibus quibus laxae arteriae adhaerent, simul 
 • Ccmrs d’Anatomie Medicate : tcm. iii. p. 126 . 
 
Arterial PaUe. 
 
 97 
 
 ft fit lit, preecipue si distensioni non facile cedunt, 
 “ loco moveantnr. Id omne pulsum yocant, 
 “ ictum, pulsationem vel micantem arteriarum 
 “ motum.”* Under the term pulse, therefore, 
 Soemmerring includes the three co-operating 
 Circumstances, in an artery, of dilatation, elonga- 
 tion, and locomotion. 
 
 On reference to the physiological writers of 
 our own country, we shall find an universal co- 
 incidence in the opinion of the dilatation and 
 contraction of arteries by the systole and diastole 
 of the left ventricle. 
 
 Thus Hales; “Now this velocity is only the 
 “ velocity of the blood at its first entering into 
 “ the aorta, in the time of the systole ; in con- 
 “ sequence of which, the blood in the arteries, 
 “ being forcibly impelled forward, with an ac- 
 “ celerated impetus, thereby dilates the canal 
 “ of the arteries, which begin again to contract 
 “ at the instant the systole ceases.”f After- 
 wards, reasoning on the same principle, and 
 assuming that “ the systole is nearly one third 
 “ of the time between pulse and pulse,” he 
 concludes, that “ the other two thirds of that 
 “ time must be spent in the contraction of the 
 * De corporis humani fabrica; tom. v. p. 84,85. 
 f Haemastatics ; p. 22, 23. 
 
 H 
 
98 The Nature and Cause of the 
 
 “ arteries ;” and, therefore, that “ the sum of the 
 “ dilatation of all the arteries in each systole is 
 “ equal to about the quantity of two-thirds of 
 “ the blood which is thrown out in each systole.”* 
 John Hunter, so original, and usually so 
 accurate with regard to phaenomena which fell 
 under his own observation, is, on this subject, 
 strangely wavering and inconsistent. Thus, 
 in his work on inflammation; “ Arteries during 
 “ their diastole, which arises from an increased 
 “ quantity of blood being thrown into them, 
 “ increase much more in length than width. — 
 u It is, however, the increased diameter that 
 “ becomes sensible to the touch. — The dilata- 
 “ tion of the artery producing- the stroke is 
 “ either felt by the finger, or may be seen when 
 “ superficial; but -were we to judge of the real 
 “ increase of the artery by this, we should deceive 
 “ ourselves ; for when covered by the integu- 
 “ ments, the apparent effect is much greater 
 “ than it really is in the artery itself ; for in 
 “ laying such an artery bare, the nearer we 
 “ come to it, the less visible is its pulsation ; and 
 “ when laid bare, its motion is hardly to be 
 “ either felt or seen. The more an artery is 
 “ covered, especially with solid bodies, the more 
 ** Ibid. p. 23, 24. 
 
Arterial Pulse. 
 
 99 
 
 “ is the pulsation to be felt or seen.”* Again, 
 “ This increase of the artery is so manifest, 
 <£ as to be felt or seen ; and produces what is 
 “ called the pulse. ”f 
 
 This alternate dilatation and contraction, the 
 author considers as a cause of equalizing the 
 circulation. 
 
 More recently, the very learned physician and 
 profound mathematician, to whom I have before 
 alluded, J assuming as a fact the dilatation of the 
 arteries at each systole of the ventricle, has sup- 
 posed an assignable proportion of that dilatation 
 in arteries of different orders of diameter. It 
 is, however, true, that this acute writer has se- 
 parated the supposed dilatation from the tangible 
 pulse of arteries, which he has shortly explained 
 nearly in the just manner. § 
 
 Lastly, the writer of the article Circulation in 
 Rees’s new Cyclopaedia observes ; “ We admit 
 “ a diastole of the arteries, arising from the 
 “ lateral pressure of the blood forcibly projected 
 <e into these canals.” Again, under the article 
 Pulse ; “ The pulse is well-known to consist of 
 “ the successive dilatations and contractions of 
 “ the arteries, in consequence of the successive 
 
 * On the Blood, &c. p. 175. f Ibid. p. 1 76. + P. 48 , 
 
 § Philosophic. Trans. IS09, p. 21,22. 
 
 H 2 
 
100 
 
 The Nature and Cause of the 
 
 “ impulses given to the blood through them by 
 “ the repeated contractions of the heart, and 
 “ by their own muscular and elastic powers.” 
 
 As this work is a recent one, emanating from 
 the metropolis, the opinion expressed in it, as to 
 the derivation of what is usually called the Pulse, 
 from the dilatation of the artery, is probably 
 that which prevails in the southern parts of 
 this island. 
 
 To the theory of Hunter, above quoted, 
 many a priori objections immediately occur. 
 For, first, if the dilatation of an artery is not to 
 be judged of by the sight or touch, it is difficult 
 to understand in what mode it can be judged 
 of at all. How, also, in an artery laid bare, a 
 dilatation, which can scarcely be seen or felt by 
 a part like the finger, should become both visi- 
 ble and tangible by the simple interposition of 
 other substances, whether soft or hard, is ut- 
 terly incomprehensible. Neither is it true, in 
 fact ; for no one ever felt a pulse in a living 
 body at all the better, because a thick garment, 
 or a steel gauntlet, intervened between the artery 
 and the scrutinizing finger. On the contrary, 
 the pulse of an artery, other things being equal, 
 is better felt, and as this able physiologist him- 
 self acknowledges, better seen, when it is super- 
 
Arterial Pulse. 
 
 101 
 
 ficial, than when it is deep. Thus, the pulse in 
 the radial artery is better felt than that in the 
 carotid ; that in the carotid better than that in 
 the popliteal ; the last better than that in the 
 femoral; and so on.* And while the pulse 
 in the first is often visible, that in the femoral 
 cannot be seen at all. Hence it follows, that it 
 is not the mere intervention of any substance, 
 that makes the pulse of the artery more tangible 
 or visible ; but some other circumstance, casu- 
 ally accompanying this intervention. 
 
 It seems, therefore, in various physiological 
 views, well worthy of inquiry by due experiments 
 on living animals, whether any such dilatation, 
 as is usually supposed, does really exist. 
 
 Nor, is this a question of pure philosophical 
 curiosity. It involves a point of great conse- 
 quence in the practice of modern surgery; of 
 which, the treatment of arterial maladies forms 
 an equally extensive, difficult, and important 
 part. Were we, for example, to suppose a case, 
 in which a young surgeon, taught to expect 
 that he should be able to distinguish, by this pre- 
 tended dilatation, an artery, which he was re- 
 
 * It is doubtless for this reason, that, in old or thin 
 persons, the pulse is, cceteris paribus, stronger, and appa- 
 rently fuller, than in those who are younger or more fat. 
 
102 
 
 The Nature and Cause of the 
 
 quired to lay bare, should, during- an actual 
 operation, unfortunately find this test to be 
 wholly wanting ; or another case, in which, a 
 more experienced operator, about to tie a deep- 
 seated artery, should be unable to discover that 
 artery by the touch, and, having made his liga- 
 ture, should be ignorant whether it was rightly 
 applied, till he was assured of his success by the 
 event ; if these cases are possible, it is surely 
 proper, that the cause of such failures should be 
 fully ascertained, and some principles esta- 
 blished, by which their future occurrence may, 
 with moral certainty, be prevented. 
 
 In the first experiments made in the year 
 1811 ,* on the arteries of living sheep and rab- 
 bits, for the purpose of observing the functions 
 of the sympathetic and vagi nerves, and the 
 effects of ligatures, Mr. George Norman and 
 I were astonished to observe, that, contrary to 
 our preconceptions, the carotids, when exposed 
 to view, were perfectly free from all dilatation 
 during the systole of the left ventricle of the 
 heart. In reality, they appeared precisely like 
 solid dead cylinders ; except that they had a 
 longitudinal locomotion backwards and for- 
 wards, exactly corresponding with the respira- 
 
 * Tliesc experiments are not detailed in this work. 
 
Arterial Pulse. 
 
 ioa 
 
 tions ; so that they were drawn backwards to- 
 wards the thorax at each inspiration, and re- 
 turned forwards to their former place at each 
 exspiration. This coincidence was farther 
 proved, by counting- with a watch indicating- 
 seconds ; Avhich, in one example, shewed the 
 respirations, and, consequently, the pairs of these 
 long'itudinal movements, to amount to 84 in a 
 minute ; w'hile, during the same space of time, 
 the pulsations in the artery were 108.* When, 
 also, the animal for a few seconds ceased to 
 breathe, the long’itudinal motion entirely ceased, 
 but returned immediately with the breathing. 
 During these short exemptions from respiration, 
 though the pulse w r as going on as before, there 
 w r as no dilatation, or other movement, in the ar- 
 tery. Precisely the same quiescence occurred, 
 when the carotid -was drawn laterally out of 
 its place. 
 
 In a sheep, which is a very timid animal, 
 the agitation of respiration during these opera- 
 tions, though much varying in different indivi- 
 duals, is usually extremely great. The dia- 
 phragm, w hich is the chief organ of that function 
 in these quadrupeds, is moved up and down 
 very forcibly and quickly. We can easily un- 
 # Experiments I. II. III. and other?. 
 
104 
 
 The Nature and Cause of the 
 
 derstand, how, at each descent of this muscle in 
 inspiration, the mediastinum, pericardium, heart, 
 arch of the aorta, and the single trunk, which 
 may be called arteria innominata, from which 
 spring both vertebrals, both axillaries, and both 
 carotids, should be drawn down, and return to 
 their places, at each exspiration. In reality, in 
 some of the experiments, the force of this 
 return was so great, that when a long portion 
 of the carotid was detached from all the sur- 
 rounding parts, it bent on itself, so as to form 
 a considerable curve outwards, towards the 
 back of the neck. The ascent and return 
 were, in all cases, accompanied with a corres- 
 ponding movement of the vagus nerve, and other 
 parts connected with the artery. In the femoral 
 artery, no regular movement of this sort was 
 produced but the shaking of the whole body 
 was so great, that no distinct motion of any 
 kind could be discerned, except during the inter- 
 vals of respiration, which sometimes took place. 
 
 In this respect, therefore, a sheep, though, 
 from the magnitude of its vessels, it offers 
 many advantages for such experiments, is less 
 proper for them than the dog, and more espe- 
 cially the horse, whose respiration is less affected 
 by the same cause. 
 
Arterial Pulse. 
 
 105 
 
 With regard to the quiescence of arteries, 
 except from the process of respiration, it was 
 natural to suppose, that what, after careful scru- 
 tiny, had been uniformly found to exist, should 
 have been a constant, and not a casual, occur- 
 rence. Although, however, the fact was, under 
 the existing' circumstances, precisely such as has 
 been represented, farther experiments shewed 
 thatthere was also another motion, corresponding 
 with the systole of the left ventricle, which was 
 wanting, when the artery w ? as strained by the 
 stretching out of the neck and head, but was 
 sufficiently apparent, under certain circumstan- 
 ces, when both were loosely placed. 
 
 This motion was first observed in the carotid 
 of a dog, in which, from an apparent apathy, 
 no disturbance of respiration or circulation took 
 place. The neck was in a relaxed position, 
 and no motion, dependent on respiration, was 
 perceivable, while that from the systole of the 
 ventricle was very manifest.* 
 
 In a second experiment on a dog, this move- 
 ment was also plainly seen ; and it was sug- 
 gested by Mr. Tudor, that it depended on the 
 position of the head, which was found to be the 
 case ; although in this, as in former experiments, 
 * Experiment YI, 
 
106 The Nature and Cause of the 
 
 when the jaws of the animal were stretched out 
 in a line with the neck, the movement from re- 
 spiration was alone visible.* 
 
 This rule generally obtained in numerous sub- 
 sequent experiments, as by reference to them 
 may be seen. 
 
 The mode of this movement was chiefly lon- 
 gitudinal ; so that the whole visible portion of 
 the artery advanced from the heart, during 1 the 
 systole of the left ventricle, and returned during 1 
 the diastole. Sometimes, though very rarely, 
 the whole artery moved in a lateral direction, or 
 forwards to the eye, and backwards from it ; 
 and, still more rarely, seemed to turn, though in 
 an almost imperceptible degree, on its own axis. 
 It even sometimes happened, that when the neck 
 was much bent, the carotid, if separated for some 
 length from its surrounding attachments, formed 
 itself into an arch, during the systole of the 
 ventricle, in the manner already described as 
 having taken place from exspiration. This was 
 the result of observations made on a great 
 number of arteries in sheep, horses, dogs, and 
 rabbits, in the strongest light, and aided by- 
 powerful lenses. 
 
 # 
 
 Experiment VIII. 
 
Arterial Pulse. 
 
 107 
 
 Even the longitudinal movement itself, how- 
 ever, although so common, did not always occur; 
 for in a horse, notwithstanding the neck was in 
 an easy posture, and the parts in no respect em- 
 barrassed, not the smallest movement of any 
 kind could be perceived in the carotid. Yet, 
 at the same time, Mr. Sewell, and others, felt 
 the pulse strongly beating in that artery.* 
 
 So also, in two rabbits, the abdominal aorta, 
 denuded of its peritonaea! coat, was examined ; 
 but in neither could we perceive, with a strong- 
 lens, any movement from respiration, or the 
 systole of the ventricle.-]* The same quiescence 
 occurred in the beginning of an observation on 
 the thoracic aorta of a rabbit. J 
 
 In all the above experiments, and others, in 
 the year 1812, in which is comprised the most 
 careful examination of aortae, carotids, and fe- 
 morals, amounting in all to fifty-five arteries, 
 we could not, by any mode of scrutiny, detect, 
 in any single instance, the smallest dilatation or 
 contraction from the systole and diastole of the 
 left ventricle of the heart. 
 
 This is the more extraordinary, as the far 
 greater number of the observations were made 
 
 * Experiments XX. f Exp. XI. XII. + Exp. XXV. 
 
108 
 
 The Nature and Cause of the 
 
 on the carotids, which Dumas adduces as espe- 
 cial exemplifications of the dilatation of arteries 
 from the systole of the heart. How far such a 
 dilatation may obtain in the arch of the aorta 
 in warm-blooded animals, I am unable to say; 
 as death immediately ensued in the only expe- 
 riment of this kind, which I have seen attempted. 
 
 Haller gives us some examples, in which 
 he saw certain arteries actually dilated during 
 the systole of the left ventricle, and contracted 
 during its diastole. Spallanzani asserts the 
 same of the aorta of salamanders, and land and 
 water frogs, (“ raines vertes.”) But the last cases 
 are by no means in point ; since, from his obser- 
 vations, it appears, that, in these animals, the 
 whole aorta has a fleshy and muscular coat ; and 
 is possessed of an independent power of alter- 
 nate contraction and dilatation,* though sepa- 
 rated from the heart, and taken out of the body. 
 In them, therefore, this part may be considered 
 as an accessary portion of the heart itself ; and 
 the stimulus of the blood, and other substances 
 acting on it, may excite in it a similar con- 
 traction, from which, like the heart, it returns to 
 a state of dilatation by its elasticity, in a mode 
 
 * Experiences sur la Circulation du Sang. Diss. III. 
 Exp. 146, 147, 148, 149, 150, 151, 152, 157. 
 
Arterial Pulse. 
 
 10D 
 
 exactly contrary to that affection of arteries, 
 which is supposed to produce the pulse. 
 
 Although, however, in some instances, the 
 force of the heart’s action may be sufficient to 
 cause alternate dilatation and contraction in 
 certain arteries, such a vibration cannot be ne- 
 cessary to the production of the pulse, since 
 that phenomenon can exist, in the fullest degree, 
 without it. 
 
 In microscopical experiments made by Hal- 
 ler and Spallanzani, those authors tell us, 
 that they were unable to discover any dilatation 
 from the systole of the heart, in arteries of a very 
 small size, such, for example, as of the 140th 
 part of an inch in diameter. These results 
 have, however, been judged inconclusive, be- 
 cause the extreme minuteness of those arteries 
 would not admit of any measurement of an 
 increase, which was presumed not to exceed the 
 160th part of their diameter. 
 
 This objection, however, will not hold good 
 in the case of the Sheep, in which the living 
 carotid has been observed to be ^44- °f an inch 
 in circumference, or almost one third of an 
 inch in diameter ;* and is still less valid with 
 regard to the Horse, whose carotid has been 
 * Experiment XV. 
 
1 10 The Nature and Cause of the 
 
 found to reach |-|4 au hich * n circumference, 
 or above half an inch in diameter.* In these 
 instances, in which the examination was aided 
 by a lens of a considerable magnifying power, 
 if any dilatation of the artery by the systole of 
 the ventricle, sufficient to produce the pulse, 
 had existed, it could not have escaped observa- 
 tion. Since, however, in these and all other 
 cases, the artery, when properly felt, gave to 
 the touch a pulse far more strong and distinct 
 than any which can be perceived by the finger, 
 in an artery undivested of the surrounding parts ; 
 we are unavoidably compelled to refer that 
 pulse to some other cause, than an excess of the 
 diameter of the artery, during- the systole of 
 the ventricle, above its diameter during the 
 diastole. 
 
 In the course of our experiments, in which a 
 carotid, separated from all its attachments, was 
 fully exposed to view, and yet no movement was 
 observable in it, we were sometimes equally 
 surprised to find, that, when the finger Avas pres- 
 sed against it, or even when it Avas removed out 
 of its place by the force of the finger beneath 
 it, or on one side, it Avas equally void of all pulse 
 to the touch. 
 
 * Experiment XXI. 
 
Arterial Pulse. 
 
 Ill 
 
 A frequent repetition of the same results led 
 to a discovery of what appears to be the nature 
 of the pulse itself. 
 
 The blood, in every part of the arterial system, 
 from the mitral valves, onwards through the 
 whole frame, to the right auricle, may be con- 
 sidered as a set of continuous columns, possessing 
 little compressibility, and filling the tubes in 
 which they are contained. 
 
 When, by the contraction of the left ventricle, 
 the blood included in it is forcibly expelled into 
 the aorta, all these columns receive the shock of 
 propulsion at the same instant. But the velocity, 
 during this systole, being' greater than during" 
 the diastole, the momentum, and consequently 
 the impulse, in every direction, is also greatest 
 in the systole. When, therefore, an artery is 
 compressed with the fingers, in the usual mode 
 of feeling the pulse, the blood, in consequence 
 of the systole, rushing’ into the artery with an 
 increase of momentum, gives a stronger impulse 
 of dilatation to the fingers, than from the less 
 momentum which exists during the diastole, 
 and thus produces the phenomenon of the pulse. 
 
 Hence, it appears, that the pulse is the effect, 
 not of an extension of an artery beyond its usual 
 diameter, but of a stronger effort, during the 
 
112 
 
 The Nature and Cause of the 
 
 systole of the ventricle than during- its diastole, 
 to restore the usual diameter of the arterv, 
 which had been diminished by compression. 
 
 Since, also, the excess of velocity from the 
 systole extends throughout the whole of the 
 space compressed by the fingers, it is evident, 
 that the distending effort, producing the sense 
 of pulsation, must also be felt throughout 
 that space. 
 
 Before this explanation could be fully admit- 
 ted, it was necessary to ascertain the cause of 
 the converse of this state ; or the reason why a 
 pulse was sometimes wanting in an artery ex- 
 posed to the view, and susceptible of any mode 
 of examination by the touch. Reiterated trials 
 demonstrated, that this deficiency was owing to 
 the followng circumstances. The coats of the 
 carotids are so firm, that when either impelled 
 against any soft substance, or simply moved out 
 of their place, these arteries readily recede ; 
 suffering no reduction of diameter, and, there- 
 fore, giving no sensation of a pulse. But if 
 they are confined by any hard substance placed 
 behind them, so as to resist a change of posi- 
 tion from the pressure of the finger, or if they 
 are squeezed between the finger and thumb, 
 
Arterial Pulse . 
 
 113 
 
 So as, in either case, to suffer a certain reduction 
 of diameter, then the pulse never fails to exhibit 
 itself. 
 
 These latter experiments, therefore, while they 
 shew that the pulse does not exist under the 
 mere contact of the finger with the artery, and, 
 therefore, completely refute the supposed dila- 
 tation of an artery by the systole of the ven- 
 tricle, as an object of touch ; by ascertaining 
 the precise circumstances under which a pulse 
 does or does not exist, demonstrate, beyond 
 all reasonable objection, the nature of that 
 phaenomenon. 
 
 Hence we see the probable reason, why no 
 pulse is said to have been discovered in those 
 surgical operations, to which I have before 
 alluded. If, however, the principle as to both 
 states be well established, we have only suffici- 
 ently to diminish with the finger the diameter of 
 an artery, and then, if it be of a certain size, and 
 the course of the blood through it, from the 
 heart, be unnterrupted, we shall not fail to feel 
 the pulse in that artery. 
 
 These points may be illustrated by the an- 
 nexed figures. Plate I. 
 
 i 
 
14 The Nature and Cause of the 
 
 I. Situation in which no Pulse is felt. 
 
 fig. i. 
 
 A. B. C. D. A tube of the same size as the 
 carotid, in a large living horse. 
 
 a. b. Diameter of the tube during the systole 
 and diastole of the left ventricle. 
 
 c.d.e.f. The same artery moved laterally 
 out of its place, as expressed by the dotted 
 curved lines. 
 
 </.h. The diameter of the artery, so displaced, 
 remaining exactly equal to that of the same artery 
 at a. b. 
 
 In this case, the diameter of the artery not being 
 diminished by the pressure, no pulse is felt in it. 
 
 II. Situation in which the Pulse is felt. 
 
 FIG. II. 
 
 A. B. C. D. A cylindrical artery, as in the 
 former figure. 
 
 a. b. Its natural diameter during the systole 
 and diastole of the left ventricle. 
 
 c. d. e. A given space, through which the 
 artery is compressed by the fingers, when the 
 pulse is felt in the usual way : expressed by the 
 dotted line, in which are shewn the various 
 degrees of diminution of diameter in the vessel, 
 
V 
 
 Fig: 1. 
 
 Fig: 2. 
 

 
 ‘ 
 
 
 
 * 
 
 
 
 
 
 
 
 
 ** 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Arterial Pulse. 
 
 115 
 
 by the approach of that line, c. d. e. to the oppo- 
 site and fixed side of the artery A. C. 
 
 In this case, in consequence of the increased 
 velocity of the blood during- each systole of 
 the ventricle, the pulse is felt throughout the 
 whole extent of the compressed and contracted 
 part from c. to e. 
 
 From the facts which have been stated, we 
 see the weakness of those arguments, by which 
 it is inferred, that, because arteries have, under 
 certain circumstances, a power of dilatation and 
 contraction, therefore, that dilatation and contrac- 
 tion must be produced by the usual systole and 
 diastole of the heart. The inference, in this case, 
 is just as legitimate, as if we were to conclude, that, 
 because a scale may be made to preponderate with 
 the weight of a pound, ergo it must turn with that 
 of a scruple. This error, however, is not uncom- 
 mon with those, who, deserting the plain and 
 direct road of fact, satisfy themselves with d 
 priori reasonings. In reality, arteries during 
 health are always in a forced state of dilatation, 
 which the usual impulse of blood from the left 
 ventricle is incapable of augmenting. 
 
 From the above statement, ive can also under- 
 stand, why the phenomenon of the pulse should 
 be confined to vessels of a certain diameter, or at 
 
116 The Nature and Came of the 
 
 a certain distance from the heart. In the first 
 case, the vessel, if very small,* does not, without 
 obliteration of its cavity, admit of that dimi- 
 nution of diameter, which is necessary for the 
 production of the effect. In the second case* 
 the difference of velocity of the blood in a 
 distant vessel, during- the systole and diastole of 
 the heart, is so far lost, as not to give the sen- 
 sation of a pulse to the fing-er, although, under 
 certain circumstances, it may be sensible to the 
 eye. Thus, in various of the microscopical 
 observations of Haller and Spallanzani, 
 the predominance of the velocity of blood from 
 each systole of the ventricle was very visible ; 
 and in a much more palpable instance, I have 
 often seen the blood flow from the cephalic 
 vein of a human being, with jets almost as 
 from an artery ; and yet, notwithstanding the 
 turgid state of that vein, not the smallest pulse 
 could, on the nicest examination, be discovered 
 in it. 
 
 These facts respecting the pulse point out 
 one cause of that phenomenon, which was the 
 stumbling block in the way of Mr. HunteE, 
 and still continues to be so in that of the majority 
 
 * Haller asserts, that no pulse can be felt in an artery, 
 which is less than one sixth of a line in diameter. 
 
Arterial Pulse . 
 
 117 
 
 of modern physiologists. If an artery has, 
 from the systole of the heart, no visible pulsa- 
 tion, when denuded; why has it so often a 
 visible pulsation, when surrounded with its 
 natural coverings ? 
 
 In order to discover this cause, we have only 
 to make one simple experiment. Lay bare an 
 artery, and no dilatation is perceivable. Place 
 behind it a hard substance, so as to prevent its 
 recession. Press the finger against it exactly 
 opposite to the resisting substance; and you will 
 immediately perceive the finger propelled out- 
 wards at each systole of the ventricle, and re- 
 treat at each diastole, The experiment may be 
 repeated in various ways, and will always, under 
 proper circumstances, have the same result. 
 The whole which is necessary is, that the artery 
 should have its diameter in a certain degree re- 
 duced ; and then the substance reducing* it, if 
 not too ponderous, will be driven off in leaps, 
 which must accord with the systoles of the heart, 
 and are often perceptible to the eye. 
 
 In this way, the pulsation of arteries may be 
 frequently seen, when they are unusually com- 
 pressed by muscles, or other intervening sub- 
 stances. Hence faeces in the colon, or other 
 indurations in the abdomen, near, or in close 
 
118 
 
 The Nature and Cause of the 
 
 contact with, the aorta, by compressing- that 
 vessel, often, both to the eye and touch, simulate 
 aneurysms ; and hence aneurysms themselves, 
 forming-, for the blood, channels, which are pre- 
 ternaturally compressed in various directions, 
 suffer jerks from the impulse of the ventricle, 
 which often shake all the neighbouring parts. 
 
 It is not, then, the mere intervention between 
 the eye or finger, and an artery, of any substan- 
 ces, whether hard or soft, that, conformably to 
 the opinion of Mr. Hunter, makes its pulsa- 
 tion more sensible ; but it is because the sub- 
 stances, thus intervening, often interrupt the 
 current of blood through the artery, and there- 
 fore receive a shock, which may be tangible or 
 visible, from each systole of the ventricle. 
 
 It has been suggested, that the tangible pulse 
 of an artery may arise from the impulse pro- 
 duced by the approximation of the more internal 
 coats to the external, during the systole of the 
 heart. The microscopical observations of 
 Hauler shew, that, in the smaller arteries, there 
 is in the same vessel, at different times, a very 
 considerable difference between the relative 
 thickness of the coats, to that of the light or 
 diameter of the area. Thus, in one of his exa- 
 minations of the mesenteric artery of a frog, 
 
Arterial Pulse. 
 
 119 
 
 at the commencement of the observation, the 
 coats were twice the diameter of the area, but 
 at the conclusion, the thickness of the coats 
 was only a fourth part of that diameter. This 
 difference depended entirely on the force of 
 circulation in the different cases . * Other in- 
 
 stances of this variation are recorded by the 
 same author ; but in neither of them was there, 
 at the same time, any change in the diameter of 
 the whole artery. Since, however, he is wholly 
 silent as to any thinning of these coats during 
 the systole of the ventricle, and thickening 
 during the diastole, we have a just right to con- 
 clude, that no visible change of that kind existed, 
 and therefore, that the tangible pulse is in no 
 degree owing to this cause. 
 
 A recent author having assumed that, “ the 
 11 volume of blood is greater in a given space of 
 “ an artery at one time than at another,” con- 
 cludes that the calibre of the artery must be 
 proportionably great. f Both these positions 
 
 will readily be granted ; but I am at a loss to 
 see how they prove the dilatation of an artery 
 by the usual systole of the heart; unless it 
 could be shewn, that the quantity of blood in 
 * Memoires sur le Mouvement du Sang, p. 228 . 
 t Pring’s View of the Relations of the Nervous System, p. 67 ° 
 
120 
 
 The Nature and Cause of the 
 
 the artery is greater during the systole than 
 during the diastole. This, however, I by no 
 means admit. The velocity of the blood is 
 greater, but not the quantity. 
 
 Various other a priori arguments are employed 
 in favour of this opinion of alternate dilatation 
 and contraction of arteries. Not satisfied with 
 what really is, authors boldly decide what ought 
 to be, the process, by which the circulation is, 
 on all occasions, carried on through this system. 
 They have observed, that, among the different 
 genera in the scale of animated being, there is a 
 sort of balance, by which an apparent defect 
 of power in one part is supplied by some equi- 
 valent accession in another. Some animals, 
 having no hearts, owe the circulation of their 
 blood to vascular action alone. Others, having 
 imperfect hearts, obtain assistance from other 
 parts of the vascular system. Hence, they 
 have sagely concluded, that, in all more perfect 
 animals, the heart, unassisted by that system, is 
 incapable of maintaining the healthy circula- 
 tion. Strange analogy ! Ought we not, on the 
 contrary, from that very gradation itself, to 
 infer, that, in animals with hearts so elaborate 
 and perfect as in the mammalia, the assistance 
 of the vascular system is unnecessary, in direct 
 
Arterial Pulse. 
 
 121 
 
 proportion to that perfection ? In this view, 
 therefore, the conclusion drawn from the circu- 
 lation and growth of akerious foetuses, is a mere 
 argumentum ad ignorantiam, which furnishes no 
 proof of the mode of circulation in full grown 
 and perfect animals, after exclusion from the 
 womb. 
 
 Those, who maintain that the pulse is owing 
 to the alternate dilatation and contraction of 
 arteries, from the systole and diastole of the left 
 ventricle, have probably deduced their conclu- 
 sion from the analogy of the action of the heart 
 itself. In this organ, they presume that each 
 cavity is dilated in consequence of the distending 
 power of the blood impelled into it, and then 
 contracts itself in consequence of that distention. 
 To me, however, it appears, that this theory, 
 however specious, is absolutely erroneous. The 
 different compartments of the heart are so far 
 from expanding, in consequence of the blood 
 which is driven into them, that, when altogether 
 empty of blood, and even separated from the 
 animal, they expand in a greater degree than 
 when in their natural situation during life and 
 healthy circulation. Hence, Mr. Hunter 
 himself, notwitbstandi o- the view which he 
 gives of the action of the heart, acknowledges 
 
122 The Nature and Cause of the 
 
 that this organ, after death, has a larger volume 
 than while the animal is living.* The true 
 nature of the heart’s action, if urged as an ana- 
 logical proof of that of the arterial system, 
 would therefore lead to conclusions, respecting 
 the movements of that system, very different 
 from those which are deduced by the writers who 
 advance it. 
 
 To the opinion of the want of visible alter- 
 nate dilatation and contraction of arteries, as a 
 cause of the pulse, it has been objected, that 
 this may arise from faintness, or certain other 
 circumstances of disorder in the animal, which 
 has undergone the operation of having them 
 laid bare by the knife. 
 
 To this objection, it might, perhaps, be suffi- 
 cient to reply, that it is incumbent on those who 
 adduce it, to prove the operation of such a cause. 
 But, waving that argument, I presume it will 
 be admitted, that this supposed weakness must 
 either affect the heart, and therefore the circu- 
 lation in general, or else that particular artery, 
 which is the subject of investigation. 
 
 * In his experiment with the bellows, the heart, when not 
 acting, became twice as large as when acting. On the 
 Blood, &c. p. 147. 
 
Arterial Pulse. 
 
 123 
 
 With regard to the first ground of objection, 
 so far is the action of the heart in a sheep or 
 horse from being impaired by exposing the 
 carotid, that it seems to be actually increased, 
 somewhat in frequency, and, apparently, a good 
 deal in force. This is peculiarly the case 
 during any struggle. At the same time, in all 
 the above experiments, the pulse in all other 
 tangible arteries, which lay undisturbed amidst 
 their natural integuments, was at least as strong 
 as before ; and on one occasion, a very minute 
 artery, arising from the exposed carotid of a 
 horse, having been wounded, a thread of blood 
 sprang out with such force, as to fall on the 
 ground at the distance of eight feet from the 
 punctured part. Yet, under no circumstances, 
 were we able to discover the least dilatation or 
 contraction of an artery from the systole and 
 diastole of the ventricle. 
 
 So much with regard to the state of the 
 heart ; and as to that of the vessel itself, the 
 objection is altogether nugatory, unless it can 
 be shewn, that an exposed artery is always less 
 filled by the systole than is natural, and that, 
 consequently, the pulse is either wanting, or, 
 at least, diminished in force. On the contrary, 
 in all the experiments above related, in which 
 
124 The Nature and Cause of the 
 
 the vessel retained its full size, the pulse, when 
 properly felt, was so far from exhibiting any 
 weakness, that it possessed a degree of strength, 
 of which no one, who had not examined a denu- 
 ded artery, could have had any conception. 
 
 Dumas accuses Hauler of inconsistency, 
 in denying that the circulation of the blood 
 depends on the action of the arteries, since his 
 own experiments prove the power of various 
 stimuli, applied to those vessels, to renew the 
 circulation in them after it had become lan- 
 guid, or was about to cease. “ II a vu qu’on 
 “ pouvoit ranimer et retablir son mouvement 
 “ lorsqu’ il faiblissait, ou qu’ il alloit s’eteindre, en 
 “ portant sur les vaisseaux divers moyens d’ir- 
 “ citation.”* This statement is a mere fiction. 
 Hauler expressly denies the power of any 
 chemical or mechanical stimulus to excite vital 
 contraction in an artery ; and after the most 
 careful perusal of his work, “ Sur le Mouve- 
 “ ment du Sang,” to which Dumas alludes, I can 
 find no single example of the restoration of the 
 circulation of the blood by any operation on 
 the arteries, except that of blood-letting-. The 
 same is true with regard to the experiments 
 
 * Physiologic, tom. iii. p. 305. 
 
Arterial Pulse. 12j 
 
 of Spallanzani, whom Dumas includes in 
 his reference. 
 
 The rationale of this effect of blood-lettings 
 I have already attempted to shew ; and I should 
 have been far from thinking 1 it necessary to 
 advert to it on the subject of the pulse, had not 
 Dumas fancied that it illustrated his theory of 
 that phenomenon. 
 
 On the whole, I trust that it has been proved, 
 by sufficient force of evidence, 
 
 First, that in the larg’er arteries of certain 
 animals, there is no sensible dilatation or con- 
 traction from the systole and diastole of the left 
 ventricle of the heart ; and, therefore, that the 
 pulse cannot depend on that alternation : and, 
 
 Secondly, that the chief cause of the pulse is 
 a strong- and predominant impulse of distention 
 from the systole of the left ventricle given by the 
 blood, as it passes through any portion of au 
 artery forcibly contracted within its natural 
 diameter. 
 
 I have already spoken of the longitudinal 
 movement* which, in the foregoing experiments, 
 was usually, but not always, observed in arteries, 
 from the systole of the ventricle ; and I Avas 
 desirous of examining, in a large animal, whe- 
 ther this motion was an elongation of the vessel. 
 
126 The Nature and Cause of the 
 
 or the mere propulsion of the whole artery for- 
 wards from the heart. When, however, even in 
 the carotid of a horse, the circulation was unim- 
 peded by a ligature, the whole movement, when 
 visible, was so short, even in an extent of several 
 inches, as to render abortive any mode which I 
 could devise for its mensuration. 
 
 A firm ligature round the vessel, probably by 
 resisting the free current of blood, greatly in- 
 creased the longitudinal advance of the vessel ; 
 and, in an experiment on the carotid of a horse, 
 I was able to ascertain that this advance, at 
 each systole of the ventricle, was about of 
 ail inch.* 
 
 This longitudinal movement was also increa- 
 sed in a ewe by great loss of blood, f and by 
 the approach towards death in the aorta of a 
 rabbit. J In this latter case, it remained, after 
 the cessation of breathing, as long as the left 
 ventricle continued to act. 
 
 I may add, that it was also, in several animals, 
 visibly augmented by certain irritations of the 
 sympathetic nerve ; although the detail of these 
 experiments has been omitted, as not immedi- 
 ately connected with the design of this work.§ 
 
 * Experiment XXI. f Ex P- XXIV. J Exp. XXV. 
 
 § There seems to be some connection between this longi- 
 tudinal proje&ion of arteries, arising from haemorrhage, and 
 
Arterial Pulse. 
 
 1 2o 
 
 Still, however, none of these causes of the 
 increase, of longitudinal motion produced the 
 smallest dilatation or contraction of any of the 
 affected arteries, from the systole and diastole 
 of the ventricle. 
 
 With regard to the longitudinal advance, it 
 is evidently not the result of any vital action in 
 the artery itself, but the mere mechanical effect 
 of the peculiar mode of systole in the left ven- 
 tricle of the heart. 
 
 In the course of our experiments, I attempted 
 to investigate the causes of error in Galen, 
 and some recent physiologists, who ascribe the 
 pulse to an inherent power of dilatation in 
 the arteries, independent on any mechanical 
 influence of the blood on their coats. In sup- 
 port of this principle, they adduce certain ex- 
 periments to shew that a pulse will exist in the 
 artery of a living animal, even where the blood 
 does not reach ; and, conversely, that, under 
 
 other debilitating powers, and the fa6t mentioned by Haller; 
 who relates, that, on various occasions, when, in minute 
 arteries, the predominance of the velocity of the blood in the 
 systole of the ventricle above that in the diastole could not 
 be perceived during a vigorous state of the animal, it became 
 very conspicuous, when, from the length of the experiment, 
 he was greatly exhausted.- — Memoires sur le Mouyement 
 du Sang, 
 
128 
 
 The Nature and Cause of the 
 
 certain circumstances, solely affecting - the coats 
 of arteries, it will not exist where the blood 
 reaches with full force. 
 
 The truth of the first position we tried in 
 various ways, by means of ligatures, and more 
 especially by three ligatures, distant from each 
 other, and completely obstructing the circula- 
 tion. On compressing the artery with the finger 
 and thumb beyond the first, second, or third 
 ligature, we could usually, but not always, per- 
 ceive a very faint movement, somewhat resem- 
 bling that from the impulse of the blood through 
 the vessel, by the systole of the ventricle. This 
 sense of beating was, however, greater, the 
 nearer we approached the first ligature ; and, 
 when we were at a certain distance from it, was 
 almost wholly perceived on the side of the finger 
 and thumb nearest the heart, without being 
 equally continued through the whole compressed 
 space, as happens in the case of the real pulse. 
 A feeling of impulse, similar to that last descri- 
 bed, occurred between the second and third 
 ligatures, after the space included between the 
 two first had been emptied of its blood,* and 
 even beyond the third, after the blood had been 
 
 * Experiment XIX. 
 
Arterial Pulse. 
 
 129 
 
 suffered to escape, by puncture, from both the 
 spaces included between the three ligatures.* 
 
 On the whole, there appeared to us no reason 
 to doubt, that, except in the case in which the 
 finger and thumb, placed immediately beyond, 
 and almost in contact with, the first ligature, 
 felt the direct impulse, from the heart, of the 
 column of blood through the tied part, all the 
 other sensations of pulse were merely faint per- 
 ceptions of the longitudinal movement of the 
 artery, from the systole of the ventricle already 
 described, more or less continued along the coats 
 of the vessel through the ligatures, and, of 
 course, just as strong when the blood between 
 the two first, or the second and third, ligatures, 
 had been evacuated, as when it remained in 
 the vessel. 
 
 In order to prove, that there exists in the coats 
 of arteries, a power of dilatation and contrac- 
 tion, independent of the blood which they 
 contain, Galen relates his having made the 
 following experiment. In the artery of a living 
 animal, he made a slit, into which he introduced 
 a tube, so as to nil the vessel, and prevent the 
 evacuation of the blood through the slit. A 
 pulse was now perceptible to the eye, in the 
 * Experiment XX; 
 
 K 
 
130 
 
 The Nature and Cause of the 
 
 vessel beyond the tube. But when a ligature 
 was firmly made round the vessel upon the 
 tube, the pulse beyond the tube was no longer 
 to be seen.* 
 
 This experiment we tried to repeat ; but 
 without success. It failed, in the manner rela- 
 ted in Experiment XXVII. 
 
 I am, therefore, altogether unable to decide 
 as to the truth of Galen’s relation, or as to the 
 cause of the circumstances, if they exist as he 
 states them. 
 
 It is, however, difficult to see how these 
 results, if admitted, go any way towards esta- 
 blishing the inference which he draws from 
 them ; since, if the pulse depended simply on 
 the spontaneous dilatation of an artery, there 
 seems to be no reason why an attachment of its 
 coats to an included tube in one spot should 
 prevent this spontaneous dilatation of the same 
 artery in another spot, at some distance beyond 
 the former. 
 
 Many of the authors, whom I have quoted, 
 speak of the locomotion of arteries from the 
 
 A 
 
 systole of the heart. Bichat especially cha- 
 racterizes this affection by the term redressement ; 
 
 * Galeni, An in Arteriis Natura Sanguis contineatur, 
 liber. Edit. Charterii, tom. iii. p. 163. 
 
Af ferial Pulse. 
 
 131 
 
 a term , which, in the connection in which he 
 uses it, 1 cannot understand, unless it means a 
 disposition to straitening* of vessels previously 
 tortuous, or interrupted by angles. Such a 
 tendency certainly takes place in the animal 
 frame in one remarkable instance ; which is 
 that, in which a large column of blood, driven 
 into the aorta at each systole of the ventricle, 
 tends to bring those parts towards a strait line, 
 and thus throws the apex of the heart upwards, 
 against the ribs. 
 
 Conformably to this principle, we find, that 
 if a leather tube, already stretched by a con- 
 tained fluid, is placed in a curved direction, 
 and a new quantity of fluid is forcibly impelled 
 into one end, which is fixed, while the other 
 parts of the tube remain free, it tends to assume 
 a rectilinear form. 
 
 It is not, however, easy to apply this principle 
 to vessels in the living body, which are chiefly 
 attached to surrounding parts. I have tried to 
 examine what really occurs in tortuous vessels, 
 laid bare, in living animals ; but have hitherto 
 been unable to discover any, which would be fit 
 subjects for this species of observation. The 
 spermatic artery in Rams is sufficiently tor- 
 tuous ; but is so involved in vascular substance, 
 
132 
 
 The Nature and Cause of the 
 
 that, in one attempt of this kind, our examina- 
 tion was defeated by the great haemorrhage, 
 which followed the dissection down to the artery. 
 
 In the experiments above related, it appears, 
 that, exclusively of the longitudinal motion 
 from the systole of the heart, there was occasion- 
 ally, from the same cause, a slight lateral and 
 even rotatory motion. When, however, the 
 carotid, by bending the neck, was relaxed, and 
 assumed somewhat of a curvilinear direction, 
 so far was it from being straitened by the im- 
 pulse of the blood, that the curvature was sen- 
 sibly increased. 
 
 We are told by Haller, that, in arteries 
 which formed a bend, he often saw the systole 
 of the ventricle cause the portion nearest the 
 heart to approach to that which was farthest, 
 so as to render the angle more acute.* In a 
 patient, who had suffered hemiplegia, and in 
 whom the right temporal artery was very promi- 
 nent and tortuous, no perceptible movement 
 existed in the artery, until, imitating the effect 
 of a ligature, I with my thumb compressed a 
 certain part of the vessel ; in consequence of 
 which, the part before the pressure suffered a 
 visible motion, which, on close examination, 
 * Memoires sur le Mouvement du Sang, p. 34. 
 
Arterial Pulse . 
 
 133 
 
 appeared to be an approach of the first curved 
 line, containing 1 the angle, to the next beyond it, 
 as in the case above described by Haller. 
 
 That this movement was mere locomotion, 
 and not dilatation and contraction, is, I think, 
 confirmed by its having' occurred only when 
 the artery was obstructed ; since it has been 
 shewn, with regard to denuded arteries, that, 
 when obstructed by ligatures, they suffer an 
 increase, and sometimes an entire production, of 
 locomotion, but never a dilatation and contraction. 
 
 It is highly probable, that the pulse, which is 
 sometimes visible in the arteries of living ani- 
 mals, when it does not arise from the effort of 
 the blood to remove a compressing substance, 
 is owing to this locomotion of the vessel •, which, 
 if the artery is considerably relaxed, will take 
 place in that direction, consistently with the 
 longitudinal tendency, in which it meets with 
 least resistance. Thus, in my own left wrist, 
 if I straiten the radial artery, by forcing the 
 hand strongly backwards, I can perceive no 
 movement of the vessel. But if I bend the 
 wrist, so as to relax the artery, I then, at each 
 systole of the heart, perceive in it a motion, 
 which is partly forwards towards the eye, and 
 partly diagonal between the longitudinal axis of 
 
134 
 
 The Nature and Cause of the 
 
 the vessel and the ulna. Many other instances 
 of visible pulsations of arteries, exactly corres- 
 ponding with the systoles of the heart, and 
 probably produced by a similar locomotion, are 
 observable in human beings, as in the lower 
 part of the carotids of nervous women, &c. 
 
 If the locomotion of an artery, concurring 
 with the common cause of the pulse, can in any 
 degree contribute to the occasional modification 
 of that phenomenon ; we may conceive, that, 
 under certain circumstances, it may, of itself, 
 exhibit, both to the eye and finger, somewhat of 
 a similar affection. I have already exemplified 
 one modification of this effect, in arteries ob- 
 structed by ligatures. 
 
 To this head may, 1 think, be referred a case, 
 which! have often witnessed, aud which is that 
 of a double stroke in the radial artery. From 
 among the different examples of this kind may 
 be selected the following, which not long ago 
 occurred. In a thin youth, aged 17, recovering 
 from a slight typhus fever, the systoles of the 
 ventricles, and the pulse of both carotids and of 
 the left radial artery, corresponded, and were 
 exactly 90 in a minute, while the pulse of the 
 right radial was precisely ISO ; the alternate 
 strokes differing in strength. The true stroke 
 
Arterial Pulse. 
 
 135 
 
 was sharp and hard ; and the secondary one was 
 perceptible, only when a very faint pressure was 
 made on the artery by the finger, but immedi- 
 ately and entirely vanished, either when the 
 pressure was, in a certain degree, increased, or 
 when the artery was confined in one place, below 
 the part felt, by being driven sideways towards 
 the outer edge of the radius. Twenty days 
 after, this second stroke had ceased ; the pulse 
 being 96 in a minute, and softer and fuller than 
 before. The young man was, himself, well ac- 
 quainted w ith this peculiarity of the pulse in his 
 right wrist; which, he said, he could always 
 produce by running, or other violent exercise. 
 Accordingly, several days having elapsed, when 
 I felt it after he had used a good deal of exer- 
 tion, it was 108 in a minute ; and the second 
 stroke could again be perceived, though not so 
 distinctly as before. 
 
 In this case, it seems probable, that, during 
 the systole, the impulse of blood produced some 
 locomotion in the artery, which returned to its 
 place during the diastole of the ventricle ; giving 
 to the finger a secondary impulse, similar to a 
 w'eak pulse. On this principle, it is easy to see, 
 how the prior change of place might be occa- 
 sioned by the strong or rapid impulse of the 
 
13G The Nature and Cause of the 
 
 column of blood from fever, or violent exercise 
 while no such change would occur during the 
 more undulating impulse produced by the slower 
 and gentler contraction of the systole during rest 
 and health. 
 
 If this explanation of the pheenomenon of the 
 double pulse be just, it will suggest the mode* 
 in which, it is probable, that the elasticity of 
 arteries may have led certain physiologists to 
 attribute slight occasional anomalies in the 
 pulse to an independent action of the vessel. 
 Since, however, there are various other occa- 
 sions, on which there is a difference, in point of 
 frequency, between the systole of the heart, and 
 the pulse in an artery ; and also between one or 
 both of these, and the pulse in another artery ; 
 it is necessary to enter on a more extensive 
 investigation of these varieties* 
 
 I may here begin with remarking, that, in 
 making such observations respecting the differ- 
 ence of pulses, during the same time, a little 
 more of caution seems necessary, than appears 
 to have been sometimes employed. 
 
 In the first place, the comparison must always 
 be made between arteries, the beats of which are 
 sufficiently strong to admit of being distinctly 
 felt 3 for, agreeably to a former observation, the 
 
Arterial Pulse. 
 
 137 
 
 systole of the ventricle does not always give 
 the power of producing’ a pulse to every artery 
 within its influence. So, also, an examination 
 of the pulse in two arteries in succession will 
 by no means answer the purpose. If the tact, 
 and power of attention, of the examiner, be not 
 nice, these arteries should be felt, at the same 
 time, by two accurate observers ; of whom one 
 should count aloud, while the other silently ob- 
 serves whether the beats in the second artery 
 correspond with those in the other. On most 
 occasions, however, a nice observer will, without 
 the embarrassment of arithmetical reckoning- 
 easily, at the same time, compare two pulses, 
 if they are distinct ; and if any confidence is to 
 be placed in frequently repeated observation, I 
 may venture to assert, that if the author, who 
 has drawn his example of a difference of pulsa- 
 tion from a branch of the pudic artery, compa- 
 ratively with the radial, had only felt that 
 branch with his left hand, while he felt the 
 radial artery in his left wrist with his right 
 hand, he would have found the pulsations in these 
 two arteries exactly synchronous.* 
 
 * There may be an exception to this rule with regard to 
 the pudic artery, under certain circum >tances, in which the 
 action of the accelerator muscle, whether automatic or vo- 
 
138 
 
 The Nature and Cause of the 
 
 Those who would give the arteries a pulsation 
 independent of the heart, must found their argu- 
 ments on those cases only, in which that of the 
 former exceeds in number the systoles of the 
 latter ; because various circumstances, some of 
 which have already been particularized, and 
 others of which are easily assignable, may cause 
 the number of pulsations in arteries, to fall short 
 of that of the sensible strokes of the heart. 
 
 Were we, however, unable to point out ail 
 these causes, that would be a curious kind of 
 argument, by which we should infer, that, 
 because a pulse w ? as sometimes wanting in an 
 artery, therefore the pulse, when existing, was 
 produced by the artery. Just as legitimately 
 might we conclude, that the tube of a syringe 
 
 luntarv, gives a pulse to that artery, independently of the 
 systole of the heart. This, however, is so far from proving 
 an action of the artery itself, that it actually confirms the 
 principle of the passiveness of arteries in common circulation; 
 since the pulse, in this case, is produced by the mechanical 
 effeCt of a sudden and rapid propulsion of the blood in the 
 artery, by the ryhion of a power external to the vessel, just 
 as in common circulation, it arises from the mechanical con- 
 traction of the left ventricle of the heart. In a nearly similar 
 way, a pulse may any where be produced in a long subcuta- 
 neous vein, by a strong stroke with the finger, when the 
 vein is compressed between the struck part and the heart. 
 
Arterial Pulse. 
 
 139 
 
 propelled the fluid within it, because, though 
 the piston continued to act, the fluid would no 
 longer pass. In both cases, a cex’tain condition 
 of the conduit may be necessary, altho ugh in 
 both the conduit is equally passive. 
 
 Let us, however, inquire into the particular 
 instances of this defect. In the first place, from 
 causes which it is, perhaps, impossible to assign, 
 some arteries are more readily filled than others. 
 Thus, the carotids lose their pulse last ; and, on 
 the return of suspended life, recover it first. 
 Twenty instances have occurred to me, of the 
 total loss of pulse in the radial arteries, from 
 various maladies of the alimentary canal, whe- 
 ther a considerable time before death, or under 
 circumstances that admitted of recovery ; while, 
 at the same time, the pulse in the carotids was 
 full and strong. In one instance of general 
 dropsy, the patient had no pulse in either wrist 
 for seventeen days; yet was restored to perfect 
 health. Sometimes, before death, the pulse has 
 been wanting in one radial only. 
 
 I have seen a total loss of pulse in one arm, 
 with coldness, but complete power of motion in 
 that part; wnile the other arm was warm, and 
 possessed a perfectly good pulse, but had lost 
 ail power of voluntary motion. These symp- 
 
140 
 
 The Nature and Cause of the 
 
 toms commenced suddenly, two or three davs 
 after parturition. The patient soon died, but a 
 dissection was not obtained. 
 
 In another case, a young man, labouring under 
 pulmonary hectic, was found to have lost the 
 pulse in one wrist, immediately after coming out 
 of a warm bath. Several months afterwards, it 
 had returned, though in an almost impercep- 
 tible degree. 
 
 Another patient, a female of middle age, the 
 mother of several children, affected with severe 
 cough, was apparently in a state of convales- 
 cence, and walking about her house ; when it 
 was discovered that the pulse in one arm was 
 wholly wanting. A few days afterwards she 
 died suddenly. The whole course of the artery, 
 to the aorta, was carefully examined ; but no 
 deviation from the healthy state could be per- 
 ceived in it. 
 
 If, conformably to various of the experiments 
 above detailed, the approach to death produces 
 a great degree of contraction in arteries; and if, 
 during life itself, certain parts of arteries are 
 capable of contracting themselves, even to a 
 degree equal to that produced by death; we ma\ 
 reasonably conclude, that such a contraction 
 may have taken place in the examples just 
 
Arterial Pulse. 
 
 141 
 
 mentioned, so as to prevent that momentum of 
 blood in the several arteries affected, which 
 should give the sensation of pulse beyond the 
 stricture. This defect would, however, still be 
 compatible with a considerable flow of blood 
 through the affected arteries. 
 
 In one of our experiments, the carotid of a 
 Ewe, after having been some time laid bare, 
 was found to have spontaneously shrunk in cir- 
 cumference from 444 1 ° 444 i and, 
 
 on being examined by the touch, gave a very 
 weak and soft pulse ; while a portion of the 
 same artery, situated immediately before this 
 part, and which, having been more recently ex- 
 posed, was 444 °f an inch in circumference, 
 had a very strong and full pulsation.* 
 
 In order, however, to carry this examination 
 still farther, the same carotid artery w'as redu- 
 ced, by a ligature, to somewhat less than that 
 circumference, which we supposed it would 
 probably reach by death. The pulse being 
 now felt, a little beyond the ligature, was 
 found to be very faint and weak, while it 
 continued very strong before the ligature. It 
 appeared to us, that this reduction of diameter 
 had, in both cases, so weakened the pulse in the 
 * Experiment XXVI. 
 
142 
 
 The Nature and Cause of the 
 
 more remote portions, even of this artery, as to 
 have made it incapable of being 1 felt through 
 very thin integuments. 
 
 It is highly probable, that such a reduction of 
 calibre had, in several of these patients r taken 
 place in the subclavian artery, or some of its 
 branches; although, on the principles already 
 ascertained, the complete death of the artery, 
 and the consequent restoration of its usual ca- 
 libre by elasticity, which must have existed 
 at the period of dissection, would wholly frus- 
 trate the attempt to discover, in that mode, the 
 cause of the malady. 
 
 In reality, the larger arteries in the human 
 body soon lose their contraction by tonicity f 
 for in a man aged 64, who, in consequence of 
 pressure on the brain, from astonishing fullness 
 of its whole vascular system, died suddenly, 
 late at night, on the 22d of October, 1815, and 
 who was opened the next day at four in the 
 afternoon, a ring of the right carotid artery, 
 which measured transversely . 114 - of an inch, 
 after having been stretched out with great force, 
 returned precisely to its former length. 
 
 Another cause of the failure of stroke in the 
 pulse is the state of the heart itself. We know 
 that this occurs from various causes impairing* 
 
Arterial Pulse. 
 
 143 
 
 the propulsive power of the left ventricle. Thus, 
 any obstruction of the aortic orifice may so 
 impede the efflux of blood, as to occasion more 
 or less frequent losses of pulsation, in a remote 
 branch like the radial artery, while sometimes 
 the due pulsation is perceivable in the carotid. 
 In this case, therefore, the pulse in the radial 
 and carotid does not accord ; and that in the 
 former disagrees with the stroke of the ventricle. 
 
 An additional instance of this disproportion 
 sometimes occurs ; the action of the heart, as per- 
 ceived by the hand applied to the thorax, being- 
 much more frequent than the pulse in any artery. 
 This especially happens, where there is con- 
 striction or induration in the left auriculo- 
 ventricular orifice, or annulus venosus ; in conse- 
 quence of which, the passage of the blood from 
 the auricle into the ventricle being obstructed, 
 or a regurgitation into the auricle by the systole 
 of the ventricle being permitted, the pulsation 
 of the auricle can be felt by the hand, on the 
 outside of the thorax, alternately with that of 
 the ventricle. This double pulsation occurs 
 more especially after exercise. 
 
 I have reason to believe, that a similar phee- 
 nomenon can take place without any org-anic 
 disease whatever. 
 
144 
 
 The Nature and Cause of the 
 
 In both these cases, it is obvious, that, if the 
 systole of the auricle is uniformly felt, and the 
 left ventricle duly acts, the arterial pulse must 
 be exactly one half as quick as the sensible 
 beating of the heart. On the other hand, if 
 the force, or expulsory power, of the ventricle 
 be considerably unequal, so that a stroke in 
 the artery is sometimes lost, the arterial pulse 
 will be proportionably less frequent. The con- 
 trary proportion will take place, if, every thing 
 else being natural, all the beats of the auricle 
 are not distinguishable. 
 
 These are the chief occasions on which there 
 is a diversity of quickness in the pulsation of 
 different arteries, relatively to each other and 
 the heart ; but by what connection any of them 
 prove that the dilatation and contraction of ar- 
 teries are the cause of the arterial pulse, I am 
 wholly at a loss to discover. 
 
 There is, however, another series of phseno- 
 mena, at first view similar to the double pulse 
 above described, but probably arising from a 
 very different cause. A man, much advanced 
 in years, had long suffered under what appeared 
 to be organic disease of the heart, or large ves- 
 sels, and of the liver, followed by hydropic effu- 
 sions in the thorax, abdomen, and cellular mem- 
 
Arterial Pulse. 
 
 145 
 
 brane of the lower extremities. These effects 
 had been frequently removed by blood-letting 
 and diuretics, when, at length, he was attacked 
 with an increase of difficulty of breathing, and 
 a copious spitting of blood. 
 
 During this state, as he lay on his back in bed, 
 there appeared on the left side of the neck, 
 from just above the clavicle, upwards to the 
 spot where the large cervical vessels are crossed 
 by the sterno-mastoid muscle, a strong pulsation, 
 clearly perceptible both to the eye and finger. 
 No such pulsation was visible on the right side, 
 nor did that on the left extend above the an- 
 terior edge of the sterno-mastoid muscle. When 
 the pulsating part was gently pressed, a redu- 
 plication of stroke occurred, but ceased on 
 strong pressure. The visible dilatation was 
 alternate with the tangible pulse of the left 
 carotid artery, above the anterior edge of the 
 sterno-mastoid muscle ; and the latter was syn- 
 chronous with that of the temporal artery on the 
 same side, the right carotid, and both radial 
 arteries. 
 
 From these circumstances, it is probable, that 
 the visible dilatation, in this case, occurred in 
 the left internal jugular vein, in consequence of 
 the difficult evacuation of the blood from the 
 
 
146 The Nature and Cause of the 
 
 right side of the heart, and therefore the regur- 
 gitation of that fluid into the vena cava supe- 
 rior, and subclavian and jugular veins, at each 
 systole of the right auricle. 
 
 This phenomenon must, however, be distin- 
 guished from the usual dilatation of the jugulars 
 by the act of exspiration ; since, in the example 
 before us, the visible pulsations were eighty- 
 four in a minute, while the exspirations, during 
 the same period, were only thirty-two. 
 
 Why, in this case, the pulsation was confined 
 to the left side, I know of nothing in the struc- 
 ture of the parts which can explain, and I w'as 
 not permitted by dissection to inquire. 
 
 Besides the varieties of pulse which have been 
 mentioned, there are others, which respect the 
 length of the intervals, the velocity or sharp- 
 ness, the magnitude or fulness, and the strength, 
 of the stroke. 
 
 Under the length of the intervals are com- 
 prehended the states well known by the name 
 of quickness or slowness ; and also that kind of 
 irregularity, which we often find, not only from 
 organic, but less important maladies of the 
 heart. Both modifications are immediately de- 
 pendent on the action of the heart itself. 
 
Arterial Pulse. 
 
 147 
 
 By the terms velocity or sharpness, I under- 
 stand the length of time occupied by the systole 
 of the ventricle, which may give to the huger, 
 applied to the artery, the sensation of smartness 
 or sharpness on one hand, or of deliberateness or 
 leisure on the other. It is this sharp pulse, 
 with a comparatively long interval, which seems 
 to characterize the three states of articular in- 
 flammation, dropsy, and haemorrhage ; so as to 
 produce more or less of the sensation of metallic 
 balls passing through a tube, as I have already 
 described in a former work. Some of the ex- 
 periments, which I have related, afford ground 
 for the suspicion, that the longitudinal projec- 
 tion of the artery, described in them, may have 
 some share in the production of this pecu- 
 liar pulse. 
 
 The magnitude, or fulness, of a pulse is, 
 evidently, when the artery is either large in 
 itself, or has its parietes considerably stretched 
 by its contained blood ; as, on the other hand, a 
 small pulse arises from the small dimensions of 
 the artery. We may conceive this latter state 
 to occur, when the artery is either primarily 
 slender, or is contracted, from the want of a 
 due quantity of blood, or other causes. 
 
148 The Nature and Cause of the 
 
 The hardness of a pulse depends on the 
 degree of resistance which the artery makes to 
 the pressure of the finger ; and we can easily 
 conceive, that this hardness may be chiefly at- 
 tributable to the momentum of blood in the 
 vessel from the quick and strong contraction 
 of the left ventricle ; in consequence of which, 
 it is difficult to press through the current.* 
 So, also, as, in proportion to this difficulty, the 
 finger will be apt to remain farther from the 
 centre of the vessel, and thus to reach a smaller 
 diameter of the area, there will be, in this case, 
 a feeling of that wiriness, or contraction, of the 
 pulse, on which authors so much dilate, as indi- 
 cative of inflammatory action. 
 
 The softness of the pulse, or its easy com- 
 pressibility, may arise from an opposite state 
 of the circulation in an artery, whether it be 
 large or small. 
 
 Strength and weakness of pulse seem to be 
 terms expressive of states little different from the 
 two immediately preceding. 
 
 * This efFeft of velocity, in producing a resistance like 
 solidity, may be illustrated by the current of air driven from 
 the cylinders through a small aperture into the apex of the 
 conical smelting furnace at Carron, by which, if I rightly 
 jemember, the impulse of a walking stick was resisted as by 
 a solid body. 
 
Arterial Pulse. 
 
 149 
 
 Although, however, the causes assigned for 
 these two latter states of the pulse, may have 
 a considerable share in their production, certain 
 circumstances in Experiments XX VX and 
 XXVII., to which I have already alluded, sug- 
 gest other causes as contributing to like effects. 
 In these experiments, a portion of an artery, 
 spontaneously contracted below its usual dia- 
 meter by exposure, gave the perception not 
 only of a smaller pulse, but of one which was 
 preternaturally weak and soft. These properties 
 were augmented in Experiment XXVI., when 
 the diameter of the artery was still farther re- 
 duced by a slack ligature. Now since it cannot 
 be doubted, that, in this case, the velocity of 
 the blood in the contracted portion was at least 
 as great as in that immediately before it, and 
 that the artery itself, however reduced in size, 
 was perfectly full, we seem obliged to admit, 
 that the softness and weakness of pulse depended 
 on a greater laxity and sponginess of the cellu- 
 lar coat of the vessel, in consecpience of the 
 diminished tension ; so that the progression of 
 the blood through the artery, at each systole of 
 the ventricle, was less strongly felt by the com- 
 pressing finger. On the contrary, when, from 
 the greater distention of the artery, the coats 
 
150 
 
 The Nature and Cause of the 
 
 became more firm and dense, the impulse of the 
 blood would be more perceptible, and the sensa- 
 tion of strength or hardness proportionabl.y 
 greater. This would more especially happen, 
 if, conformably to the observation of Haller 
 respecting minute arteries, the several coats of 
 the larger ones approximate more to each 
 other, when the vessel is more fully dilated. 
 
 If also, as is asserted by Haller, with regard 
 to sanguiferous vessels, arteries are sometimes not 
 full of blood, it is evident that vessels in such a 
 State, easdy yielding to the compression of the 
 finger, would give the pulse a character of pe- 
 culiar softness and weakness. 
 
 How far the capacity of the coats to transmit 
 to the finger the perception of the impulse of 
 blood in the artery, may depend on the state of 
 the vasa vasorum, I am altogether unable to 
 suggest. 
 
 Mr. Hunter supposes, that when, by exer- 
 cise, the blood is more quickly returned to the 
 heart, the left ventricle is more distended, and 
 consequently, throwing out more blood at each 
 systole, stretches the arterial system in a greater 
 degree, and therefore produces a fuller and 
 stronger pulse. * This conclusion is, however, 
 * On 'the Blood, &c. p. 145, 146. 
 
Arterial Pulse. 
 
 151 
 
 by no means justified by what occurred in the 
 foregoing’ experiments; for though, in them, 
 we found the pulse temporarily quickened by the 
 violent striisf&’les of the animal, the diameter 
 of the carotid, during that increased action of 
 the heart, remained, at each systole, just as 
 before. 
 
 If, indeed, the ventricle, as on this physiolo- 
 gist’s supposition, should thus become much 
 increased in capacity, and the aorta should not 
 readily yield, in proportion to the increased 
 quantity of blood expelled at each systole; 
 either the velocity of that blood must be sud- 
 denly and enormously augmented, or else there 
 would be danger of fatal accumulations in the 
 cavities of the heart. 
 
 On the other hand, we find, in fact, that 
 whatsoever urges the blood more quickly into 
 the heart, increases the number and sharpness 
 of its systoles ; a provision, which should seem 
 to be superfluous, were this supposed dilatation 
 of the ventricle to take place. 
 
 If, then, the heart, continuing to throw out, at 
 each systole, precisely the same quantity of blood 
 as before, only repeats those systoles with a 
 frequency and velocity proportioned to the 
 quantity of blood which it receives; no increase 
 
152 Nature and Cause of the Arterial Pulse. 
 
 of capaciousness in the ventricle would be re- 
 quired, and all the phsenomena, preceding, ac- 
 companying, and following the operation, would 
 seem to admit of an easy explanation. 
 
 The strength with which, under such circum- 
 stances, the apex of the heart strikes the side, 
 is doubtless proportioned to the momentum, 
 with which the blood is expelled at each systole 
 into the aorta. It does not, however, from 
 thence follow, that the quantity is increased. 
 The increase of velocity alone would produce 
 an increase of momentum, although the quan- 
 tity remained the same. 
 
 For these reasons, it appears to me impro- 
 bable, that any such change, as Mr. Hunter 
 suggests, occurs in the heart ; and therefore the 
 hard, strong, or even full, pulse of an artery is 
 not attributable to that cause. 
 
 The different states, which have been descri- 
 bed, include the more simple variations obser- 
 vable in the pulse of arteries ; and it is easy 
 to see different modes, in which they are capable 
 of being simultaneously combined, so as to 
 produce other varieties. 
 
 How far the theory of their causes may be 
 complete or correct, it remains for the experience 
 of others to determine. 
 
[ 153 ] 
 
 A FARTHER POWER OF 
 ARTERIES. 
 
 IN order that the reader may be enabled to 
 form an accurate judgment of a power of the 
 larger arteries, which is about to be offered to 
 his attention, it is proper that he should be ac- 
 quainted with the general disposition of the 
 arteries which supply the head, neck, and fore- 
 extremities, in sheep. 
 
 From the arch of the aorta arises, nearly at 
 right angles, one trunk only, or innominata 
 from which, after a short distance, springs, on 
 each side, either a single vessel, dividing into 
 various branches, or a congeries of vessels, more 
 or less from a common root.f These vessels 
 
 * Plate II. Fig. I. A. 
 
 f Ibid. 3. 3. 
 
154 
 
 A farther Power of Arteries . 
 
 vessels consist of the axillaries, the mammaries, 
 and some others, which go chiefly to the outside 
 of the neck, and fore-extremities. From some 
 one of these branches respectively, but, so far as 
 I have seen, not the same on both sides, arise the 
 vertebrals, which are usually the smallest of the 
 whole. The innominata afterwards, continu- 
 ing its course in the same vertical direction, 
 divides, like a fork, into the two carotids,* 
 which pass onwards, with little variation as to 
 diameter, throwing out only a few minute bran- 
 ches, till, just behind the angle of the lower jaw r , 
 they divide, on each side, into external and in- 
 ternal. f Of each of these common carotids, the 
 area, or light, is greatly larger than that of either 
 of the vertebrals. 
 
 The effects of ligatures, on the arteries of 
 living animals, have long excited great interest 
 among physiologists ; but although most of the 
 phenomena, respecting the coalescence of these 
 vessels, were formerly ascertained by Petit, 
 
 * Plate II. Fig. 1 . B. C. 
 
 f It is extremely difficult to account for the assertion of 
 Dr, Hales, that, in the sheep, “ both carotids rose separate 
 “ immediately from the aorta unless the wether, which he 
 examined, exhibited a most extraordinary deviation from the 
 usual arterial structure in those animals. H;cmastatics, p. 27. 
 
A farther Power of Arteries. 155 
 
 Haller, and some subsequent writers, they 
 were never systematically arranged, so as to 
 shew their true relations to each other, till the 
 appearance of the very philosophical work of 
 the late Dr. Jones . * 
 
 It is now ascertained, that when the serous 
 and fibrous coats of an artery are by any cause, as 
 especially a ligature, broken through all around, 
 the ruptured vasa arteriarum pour out f) brine ; 
 in consequence of which, the coats, if sufficiently 
 ■approximating to each other, coalesce at the 
 wounded part, and thus firmly shut up the area 
 of the artery. 
 
 Much assistance to this process is usually 
 contributed by the formation of a coagulum of 
 blood, within the artery, near the ligature. This 
 may take place on both sides ; but, in our expe- 
 riments, was always found between the ligature 
 and the heart, as if it were there most wanted, 
 as a barrier against the disuniting effects of the 
 blood propelled by ihe systole of the ventricle. f 
 This coagulum varies in length from a quarter 
 of an inch to an inch, or more ; taking the form 
 of the vessel in which it is included, but with 
 which it does not appear to unite, although 
 * On Haemorrhage, &c. 
 f Experiments XVII. XXII. XXIII. 
 
156 
 
 A farther Power of Arteries. 
 
 it slightly adheres to the fibrine at the point of 
 coalescence of the artery. 
 
 These processes have been observed to occur 
 in a very short time after the formation of the 
 ligature. In the experiment above, No. XVII., 
 they were completed in seven days : in Experi- 
 ment XXIII., in less than forty hours. Dr. 
 Jones relates an instance, in which the humeral 
 artery of a dog had cohered after an interval 
 of only twenty -four hours.* 
 
 The quantity of fibrine, which is adequate 
 to the production of this cohesion, is very small. 
 In our experiments, it could not be perceived 
 in the artery, till the attached parts had been 
 forcibly disunited. 
 
 Soon after this period, the contraction of the 
 tied artery, which had begun near the ligature, 
 usually increases to entire obliteration; which 
 reaches to a greater or less extent on each side, 
 according to the power of substitution of circu- 
 lation, afforded by branches arising from the 
 same trunk. It has been supposed, that part of 
 this contraction may depend on an inflammatory 
 process, which takes place between the coats of 
 the arteries themselves ; but the chief agent is, 
 probably, the tonicity of the fibrous arterial coat. 
 
 * P. 139. 
 
157 
 
 A farther Power of Arteries. 
 
 From the experiments of Dr. Jones, we also 
 learn, that the wounded cellular membrane, sur- 
 rounding' the artery, usually pours out more or 
 less of fibrine, which gives additional strength 
 to the artery in the neighbourhood of the 
 tied part. 
 
 Amidst these processes, another takes place 
 in the cellular coat of the artery, which, in con- 
 sequence of the compression by the ligature, 
 undergoes suppuration ; and it is evident that 
 this suppuration must extend to the complete 
 division of the artery, in all those cases, in which, 
 as not uncommonly happens, the ligature comes 
 away round and unbroken. 
 
 The ultimate reduction of volume, in the 
 obliterated part of the artery, is said to be, in 
 many cases, so great, that nothing remains but 
 a mere filament, scarcely, if at all, distinguish- 
 able from the cellular substance, with which 
 it is blended. 
 
 When, in a living animal, an artery leading 
 to any part has been thus obliterated, it is well 
 known, that a quantity of blood, sufficient for 
 the performance of the functions of the part, 
 is usually conveyed by collateral trunks, or 
 small branches given off nearer to the heart 
 than the point of obliteration. These are 
 
158 
 
 A farther Power of Arteries. 
 
 dilated at first, according to the necessity of the 
 case ; but, in process of time, a few only, be- 
 come permanently distended, supei'seding the 
 rest, which collapse in different degrees, when 
 no longer required for the purposes of circula- 
 tion. Many facts of this kind, are collected in 
 the late valuable wrnrk on the Diseases of 
 Arteries and Veins, by Mr. Hodgson. 
 
 Neither in that work, however, nor in any 
 which has preceded it, can I find the least 
 mention of another benevolent provision, for 
 the same purpose, by the wise and all-powerful 
 Author of nature. 
 
 On the 27tli of September, 1815, Mr. G. 
 Norman tied both carotids of a Ram, three 
 years old, each with a single ligature. No in- 
 convenience appeared to have been sustained by 
 the animal, except what might reasonably be 
 supposed to result from a painful operation. 
 
 On the 17th of October, the ligatures had 
 come away, and the wounds were completely 
 healed.* 
 
 On the 7 v th of August, 1815, this ram was 
 killed, by opening the aorta from abo^e. The 
 weather being very hot, he was almost imme- 
 
 * See above, p. 1,3, 5. 
 
A farther Power of Arteries. 159 
 
 diately injected ; and the parts were, as soon as 
 possible, dissected by Mr. Coombs. 
 
 Notwithstanding the shortness of the time 
 which had elapsed subsequently to the death of 
 the animal, and which probably occasioned the 
 injection on the right side to fail, that on the 
 left had run extremely well, and exhibited the 
 extraordinary construction, which is very accu- 
 rately represented in Plate II. engraved from 
 drawings made from the object, on the 8th of 
 August, by Dr. Charles Parry.* 
 
 In this Plate, Fig. I. 
 
 1. Refers to the Trachea. 
 
 2. 2. 2. 2. Adjacent muscles. 
 
 A. The common arterial trunk, or Xnnominata, 
 
 arising from the arch of the aorta. 
 
 3. 3. The roots of the various arteries of the 
 
 neck, &c. before-mentioned. 
 
 B. The right carotid. 
 
 C. The left carotid. 
 
 D. The spot where, probably, the ligature on 
 
 the left carotid was made. 
 
 E. toF. The extent to which, it is probable, 
 
 that the old portion of the artery was 
 
 * The drawing is rather less than nature, and the objeft 
 is represented as somewhat fore-shortened. 
 
160 A farther Power of Arteries. 
 
 obliterated; its place being supplied by five 
 new ramifications, uniting, in different 
 points, the extremity of the inferior portion 
 of the old artery, with the superior portion. 
 
 Since some of the points of union above are 
 considerably distant from what looks like the 
 abrupt termination of the upper portion of the 
 artery, it is not improbable, that as much of that 
 part of the artery as extends nearly from D. to 
 F. and is equal in size to other parts of the 
 vessel, is itself a regeneration of the entire 
 artery; which, if it had completely met the 
 inferior portion, might have wholly superseded 
 the small new branches, and have caused them 
 to be obliterated, as no longer useful. This, 
 however, I offer as a mere conjecture, to be con- 
 firmed or annulled by future and more long 
 continued trials. 
 
 Plate II. Fig. II. 
 
 This is merely an enlarged, and somewhat 
 different outline view of the newly generated 
 vessels, with similar referential letters. 
 
 To this conclusion, as to the new creation of 
 vessels in the case before us, objections have 
 been raised, with an ardour, which has certainly 
 
161 
 
 A Jcirtlier Power of Arteries. 
 
 reached the utmost limits of philosophical can- 
 dour. Thus it has been argued, 
 
 First, that these communicating branches 
 must have previously existed, although they were 
 not noticed. 
 
 This is an objection, which could be made 
 only by those, who are unacquainted with the 
 structure and relations of the carotid arteries in 
 sheep. I have assisted at a careful examination 
 of thirty-four of these. They may, with facility, 
 be dissected for several inches from all their 
 connections, whether of nerves or cellular 
 membrane. Several fingers may be placed 
 under them : they may be drawn out, so as to 
 project an inch or two from their natural seat, 
 and may be examined all around, as easily and 
 as distinctly as dead cords. Under these cir- 
 cumstances, it would be absurd to suppose, that 
 a plexus of vessels could ever be mistaken for a 
 single trunk ; or that such vessels, projecting as 
 they do all around from the main line of the 
 artery, could have been separated from the sur- 
 rounding parts, without being wounded by 
 the knife. 
 
 But, it is said* they were too small to dis- 
 charge blood ) and only became enlarged, when 
 
 M 
 
1'62 
 
 A farther Potter of Arteries. 
 
 their enlargement was rendered necessary by 
 a ligature. 
 
 This argument, then, implies, that a main 
 trunk existed, from which these several rami- 
 fications extended, uniting the different parts of 
 the artery by additional communications, which 
 became apparent only when the trunk was 
 destroyed. 
 
 There is, evidently, only one view of the case, 
 to which this argument can possibly apply ; and 
 that is, the supposition that the ligature was 
 made on the artery within the extent of these 
 ramifications. In what mode, however, a liga- 
 ture could be applied to a round large vessel, 
 included within such a plexus of collateral arte- 
 ries, without that plexus being either cut or seen, 
 it is for those to explain or conceive, who make 
 the objection. 
 
 If, however, we for a moment admit, that 
 some of these vessels, though cut, did not, on 
 account of their minuteness, pour out blood; they 
 certainly ought to have done so, when, on ac- 
 count of the ligature on the corresponding trunk, 
 an immediate necessity was produced for the 
 transmission, through them, of a greater quantity 
 of blood, and for their consequent enlargement. 
 
A farther Power of Arteries. 163 
 
 Notwithstanding’, however, in the various ex- 
 periments on the carotids of living 1 sheep, which 
 I have witnessed, twenty-four lig-atures have 
 been at different times employed, I have never 
 seen any such plexus of vessels as that which 
 this hypothesis suggests. The arterial branches 
 given off by the carotids are, in reality, very few ; 
 but where they have existed, they have been 
 easily enough seen, and have been readily se- 
 cured by ligatures. 
 
 While, therefore, I contend, that no such 
 plexus of vessels naturally occurs in the carotids 
 of sheep, I would ask, whether any instance of 
 a similar arterial structure is to be met with, on 
 any other occasion, in the sj^stem of warm- 
 blooded animals? In the anastomoses of arte- 
 ries, the minute branches of one artery unite 
 with those of another, or may even, occasionally, 
 form circles among themselves ; but I am not 
 aware of any example, in w’hich small branches, 
 leaving a trunk, have, at the distance of one or 
 two inches, returned again into the same trunk. 
 If, therefore, such a structure is absolutely new, 
 this argument is of that kind, which would solve 
 one difficulty by a greater ; or which, according 
 to the language of the schools, would explain 
 ignotum per ignoiius. 
 
 M 2 
 
164 
 
 A farther Power of Arteries. 
 
 if,, nevertheless, it be contended, that this 
 plexus originally existed without any collateral 
 trunk ; then I would ask, why it was not rendered 
 impervious, and destroyed, by the ligature, as 
 happens to other vessels, which have undergone 
 a similar operation. 
 
 The same answer will apply to those who 
 argue, that these vessels existed in the coats of 
 the artery themselves, and, when the portion of 
 the vessel beyond them was tied, served to 
 carry the blood from the cavity of the artery 
 before the ligature, to that beyond it. 
 
 This theory presumes, that the arteries of the 
 coats, or vasa vasorum, take their rise from the 
 cavity of the trunk itself ; which, indeed. Por- 
 tal asserts to be the case, with regard to some 
 of the arterise arteriarum of the aorta. Mr. 
 Hunter, however, expressly denies this struc- 
 ture to exist in the carotids, as he was never 
 able to make the finest injection into those arte- 
 ries enter the vessels of their coats. 
 
 The argument, however, is, in every view, al- 
 together nugatory ; since a ligature on the artery, 
 before such a set of vessels, would either not influ- 
 ence, or else destroy, them; and a ligature on, or 
 beyond them, must cut off all communication 
 between the vessels of the coats, just as effectually 
 
A farther Power of Arteries. 165 
 
 as it intercepted the flow of blood in the main 
 artery itself : so that this very theory must as- 
 sume the production of new vessels, for the 
 purpose of restoring- the lost communication. 
 
 But it has been said, that the ligature was ap- 
 plied in some other part, and that this plexus 
 was a lusus naturae, altogether unconnected with 
 the effect of any operation. 
 
 This term, lusus naturse, is an extremely con- 
 venient mode of cutting a knot, which we have 
 not the ingenuity or the patience to untie. Since, 
 however, it is a mere gratuitous assertion, inca- 
 pable of proof, and unproductive of any expla- 
 nation of the phenomena; we can hardly 
 suppose that it demands a serious answer, when 
 the phaenomena themselves are capable of being 
 somewhat analogically, and therefore reasonably, 
 explained. 
 
 That a ligature should have been carefully 
 made on an artery, like the carotid of a sheep, 
 without producing some effect on the organiza- 
 tion of the vessel, will hardly be asserted by any 
 experienced anatomist. It is even well known, 
 that a moderate degree of pressure, by a fine 
 ligature, will often cut through the serous and 
 fibrous coats ; in which case, as complete a coa- 
 lescence of the parietes of the artery will 
 
166 A farther Power of Arteries. 
 
 sometimes ensue, as if the ligature had been 
 retained in its place, and produced the usual 
 chain of effects, Although, however, this liga- 
 ture was, in the case before us, actually applied, 
 and was observed to have been retained to at 
 least the thirteenth day ; yet, throughout the 
 whole course of the artery in question, no spot 
 could, after the most careful examination, be 
 found, on which a ligature could have acted, 
 except the individual part to which I have re- 
 ferred its effects. Every other portion of the 
 vessel wassmooth, equal, and completely pervious, 
 In this process of reproduction, there is a 
 considerable degree of analogy with certain 
 well-known phenomena of the animal frame. 
 If a muscular part be wounded, and the parts 
 properly applied to each other, coagulable 
 lymph, now better known under the name of 
 fibrine, is poured out, and serves as a matrix, 
 through which new vessels shoot, and unite the 
 separated portions. So, also, if a loss of sub- 
 stance occur in any one of various textures, 
 so that the defect prevents the apposition of the 
 extremities of the old part, we usually see 
 this loss, in a greater or less degree, supplied by 
 the application of new substance, of which ves- 
 sels form a due proportion, and are so disposed 
 
167 
 
 A farther Power of Arteries. 
 
 as to re-unite those previously existing 1 . This 
 effect is the real result of the process, whatever 
 be its mode ; for it matters not whether new 
 vessels begin, by a sort of crystallization, in the 
 centre of the intervening- fibrine, and find their 
 way on each side into the old vessels ; or the 
 latter vessels shoot out, so as to meet in the cen- 
 ter ; or, lastly, a combination of these two pro- 
 cesses occurs, so as to complete the march of 
 the circulation. In either case, the fact, with 
 regard to the intermediate part, is precisely the 
 same; and carry the objection ever so far back, 
 even, if you please, to the aorta at one termina- 
 tion, and tire capillaries at the other, there must 
 either be some point at which the new vessels 
 communicate, at each end, with the old, or else 
 you are reduced to the still farther absurdity of 
 supposing the creation of an entirely new san- 
 guiferous system, throughout the animal, every 
 time he accidentally suffers a loss of substance 
 of a few lines in diameter.* 
 
 * It is carious, that, on this subjedt, the zeal of scepticism 
 has even denied the existence of newly-formed arteries in 
 granulations. It would be hardly less unreasonable to deny 
 that they contain blood ; because, by whatever channels 
 this blood is carried to that substance, and continues to nou' 
 rishit, such channels, by whatsoever name we may choose to 
 call them, so far perform the functions attributed to arteries. 
 
168 A farther Power of Arteries. 
 
 The process of formation, in the new rami- 
 fications before us, seems extremely similar to 
 that just described. Dr. Jones, and other 
 writers, speak of an effusion of lymph round the 
 external part of an artery suffering - a lig-ature. 
 If this is an universal occurrence, during - a favo- 
 rable progress of recovery, it is not improbable, 
 that such an effusion may form a proper nidus, 
 in which new vessels may shoot, so as at both 
 extremities to unite the old one in such a 
 manner, as to perform the due functions of cir- 
 culation. This reproduction of artery would 
 thus be conformable to the benevolent and pow- 
 erful agency of the Creator, by which bone is 
 formed, in order to repair the loss of bone, mus- 
 cle of muscle, nerve of nerve, &c. ; these several 
 new parts ultimately performing the functions 
 of the old, though, perhaps, with somewhat less 
 of perfection as to their structure and powers. 
 
 In the explication which I have given of the 
 first figure of the second plate, I have suggested 
 the probability of a formation from both ends 
 of the obliterated artery, This has been denied 
 with regard to the more distant portion, on the 
 supposition, that no adequate arterial impulse 
 exists in that part. Such a supposition is, 
 however, contradicted by the fact ; for it appears 
 
A farther Power of Arteries. 169 
 
 from Experiment XXII., that when, by cutting- 
 through the artery between two ligatures, the 
 more direct impulse of the heart on the blood 
 was intercepted, there was a strong retrograde 
 motion of the blood in the more distant portion 
 of the artery, evidently following the round of 
 circulation by the anastomoses, and according 
 wdth each systole of the ventricle. This fact, 
 which was too palpable to admit of any mistake, 
 wholly obviates the theoretical objection last 
 stated. 
 
 The disappearance of the old portion of the 
 artery, and of the fibrine in which the new 
 plexus may have been formed, is conformable to 
 the order of facts already described, and which 
 is now generally admitted by physiologists. 
 
 Although, however, this was the probable way, 
 in which, in the example which we are investi- 
 gating-, the new generation of artery took place, 
 I am by no means prepared to assert that it was 
 the real one ; the proper demonstration of this 
 fact requiring, not only that a considerable 
 number of animals should be subjected to the 
 experiment, but that the parts should be care- 
 fully examined at various periods after the ap- 
 plication of the ligatures. 
 
170 
 
 A farther Power of Arteries. 
 
 The last objection, which it may be worth 
 while to mention as having been made to the pro- 
 duction of small vessels, for the purpose of sup- 
 plying the place of an useless trunk, is, that the 
 process is altogether new in the animal frame. 
 
 In order to give any w eight to this objection, 
 it is incumbent on those who make it, to shew, 
 that, in other cases, in which the same previous 
 circumstances have existed, the same effect has 
 not followed. 
 
 Who, however, is there, that has had oppor- 
 tunity and patience to make a similar experi- 
 ment? Who, after having fixed ligatures on 
 both carotids of a sheep, has waited a year, in 
 order to witness the result of the trial ? 
 
 In the mean w hile, I have shewn a considerable 
 degree of analogy between this case, and that 
 of the common reproduction of various animal 
 textures. 
 
 But were it even true, that no analogy existed, 
 shall w ? e, for that reason, deny the fact ? On this 
 principle, no discovery of any new phenomena 
 in the material world could ever be made. 
 When Sir Humphry Davy first exhibited 
 Potassium, had any one even suspected that 
 Potassa, an alkali, w r as a metallic substance 
 combined with oxygen ? Such a conclusion 
 
A farther Power of Arteries. 
 
 271 
 
 was not only not conformable to experience, 
 but directly contrary to all presumed analogy. 
 And yet, when the fact was seen, it was without 
 difficulty admitted. 
 
 In order farther to investigate this subject, 
 let us consult the work of Mr. Hodgson, which 
 is, certainly, a very copious and accurate maga- 
 zine of facts. Among the several arteries, which 
 are there adduced, as having been the subjects of 
 ligature, or of accidents producing obliteration, 
 in man or brutes, are the femoral, the popliteal, 
 the iliac, the subclavian, the axillary, the brachial, 
 the carotid, and the aorta. In all these cases, 
 except the last but one, the circulation is said 
 to have been carried on by various branches, 
 either known or supposed to have previously 
 existed ; and w hich, anastomosing with other 
 branches, restored the circulation in an adequate 
 degree, usually even to the trunk of the vessel 
 beyond the obliterated spot. This happened, in 
 various instances, even to the aorta itself. 
 
 With regard, however, to the common caro- 
 tid, we know that, both in man and brutes, it 
 has few anastomosing branches, till it unites, 
 within the cranium, with its corresponding 
 carotid, and w'ith the vertebrals. Among the 
 few examples in man, in which this artery has 
 
172 A farther Power of Arteries. 
 
 been tied, or otherwise obliterated, I can find 
 none, in which the mode of the vicarious supply 
 of blood has been traced by dissection. Mr. 
 Hodgson, indeed, suggests, that, exclusively 
 of the large anastomoses within the cranium 
 itself, the upper part of the carotid may be 
 supplied with blood from the anastomoses of the 
 carotids with each other, and with the subcla- 
 vian arteries ; and he mentions an instance of 
 a Dog, in which, several months after both ca- 
 rotids had been tied, “ the vertebral arteries 
 “ appeared rather larger than natural, and 
 “ branches which arose from the superior por- 
 “ tion of the obliterated carotid arteries, anas- 
 “ tomosed freely with others that were given 
 “ off by the vertebral, cervical, and subclavian 
 “ arteries.”* 
 
 Although, however, in this instance, after a 
 ligature on both carotids, a quantity of blood, 
 sufficient for the purposes of the brain, was, in 
 the dog, conveyed to that organ by the enlarge- 
 ment of some arteries, and the anastomoses of 
 others; it by no means follows, that a similar con- 
 sequence must necessarily ensue from the obli- 
 teration of the same arteries in other animals. 
 
 * P. 244 . Rather axillary arteries. A Dog has no clavicle. 
 
A farther Power of Arteries. 173 
 
 In fact, all the authors who have treated this 
 subject in Great Britain, seem to have consi- 
 dered the dog as an animal nearly exempt from 
 all the evils which might a priori have been 
 expected to flow from so important a change in 
 the arterial circulation. 
 
 From the experiments which I have related, 
 it appears, that in the sheep, the sudden destruc- 
 tion of a large part of the communication 
 between the heart and the brain is by no means 
 always a matter of such perfect indifference. 
 In a full-grown Ram, in which, some years ago, 
 Mr. George Norma nt, in my presence, made 
 a ligature on both carotids, without including 
 either of the nerves, the immediate effect of 
 the operation was so strongly felt by the animal, 
 that we judged it expedient to kill him shortly 
 afterwards. In Experiment XVII., an accurate 
 account has been given of the effect of this ope- 
 ration in a younger Ram, from the beginningto 
 the death of the animal. 
 
 It seems, therefore, that, in the sheep, there 
 is a necessity for the reproduction of carotid, 
 which, perhaps, may not exist in other vessels, 
 or, possibly, not to the same extent in the dog, 
 er certain other animals. 
 
174 
 
 A farther Power of Arteries. 
 
 Is it, however, absolutely certain, that, on 
 various occasions, arteries, which have been 
 considered as mere anastomosing - branches, 
 brought into specific notice by enlargement, 
 may not have been actual new productions ? 
 That this may sometimes have been the case, 
 there is considerable reason to suspect. 
 
 Dr. Jones* relates the case of a Dog, the 
 left carotid of which had been divided between 
 two ligatures. Forty-nine days after, a consi- 
 derable extent of the artery was found oblite- 
 rated, and the right carotid evidently enlarged. 
 An artery also, arising from the angle at the 
 origin of the two carotids, passed up on the 
 
 * Chap. iv. Seft. I. Experiment XIII. PI. xv. In the descrip- 
 tion which this author gives, he is guilty of an anatomical 
 error, when he states the carotids as arising from the arch of 
 the aorta. In the dog, the aorta first gives off a large vessel, 
 which may be called Innominata. This is curved to the 
 risrht, and from its curvature spring together the two caro- 
 tids. The innominata, continued on, forms the right 
 axillary, from which spring the right vertebral, and various 
 other arteries. The left axiilary arises by itself, from the 
 arch of the aorta, to the left of the innominata. The small 
 subsidiary artery, mentioned by Dr {ones, does not arise 
 immediately from the aorta, but from the innominata, in the 
 angle between the two carotids. It is this innominata, 
 and not the aorta, which constitutes the large curved vessel 
 in Dr. Jones’s plate. 
 
175 
 
 A farther Power of Arteries. 
 
 right side of the oesophagus, which it crossed, 
 and anastomosed with the upper part of the left 
 carotid, where it was still pervious ; thus main- 
 taining the communication between the heart 
 and the artery above the ligature. 
 
 Having many years ago investigated, with my 
 excellent friend Dr. Jenner, the disposition of 
 the carotids, &c. in a dog, of which I then made 
 a drawing, and having found no such artery 
 as this of Dr. Jones, I was desirous of making 
 some farther experimental inquiries ; and there- 
 fore requested Mr. Coombs to inject, and 
 afterwards dissect, two other dogs. This he 
 was so obliging as to do ; and in the first, which 
 was a larg'e puppy, found a small artery situated, 
 conformably to the description of Dr. Jones, 
 near the angle of the two carotids. This artery, 
 however, so far from ascending by the side of 
 the oesophagus, was reflected downwards into 
 the thorax, where it was lost. In the second 
 dog, wdiich was considerably older, no vessel 
 whatever was to be found in or near the spot 
 described. 
 
 What then ; shall we say, that this extraordi- 
 nary structure was expressly provided, in order to 
 tepair an accident, which should happen to the 
 left carotid only, and in this individual animal P 
 
176 A farther Power of Arteries. 
 
 It is much more reasonable to conclude, that 
 this accessory artery itself was either a new 
 formation, or an old artery turned into a new 
 direction, for a new and important purpose. 
 
 Without, however, laying- any stress on this 
 supposed analogy, let us see whether the opinion, 
 which I have thus attempted to defend, cannot 
 be supported by more direct and unquestionable 
 evidence. 
 
 I have mentioned above, that, in the Ram, 
 Experiment III., the right carotid artery was 
 tied with a single ligature, on the 12th of Oc- 
 tober, 1814 j and that soon afterwards, in fight- 
 ing, this ram had the ligature torn out, and 
 suffered a considerable loss of blood. As Mr. 
 G. Norman and xnyself were present when 
 this accident happened, the haemorrhage was 
 restrained in the manner above described.* 
 This ram was killed on the 7th of September, 
 1815, f and an attempt was made to inject the 
 carotids. It succeeded very well on the left 
 side, but failed on the right. A subsequent 
 examination, by dissection, shewed the right 
 carotid changed into that state, which is exhi- 
 bited, somewhat enlarged, in Plate II. Fig. 3. 
 This figure was drawn by Mr. Coombs. The 
 * See p. 5. f See Experiment XV. 
 
177 
 
 A farther Power of Arteries. 
 
 original trunk of the artery, for something' more 
 than two inches in length, from E to F, had 
 disappeared; and for it were substituted three 
 small branches, uniting the two extremities of 
 the old artery. One of these, G, immediately 
 united these extremities. The two other bran- 
 ches were continued into a somewhat flattened 
 oval fleshy body, at D, from whence they sepa- 
 rately proceeded into the more distant extremities 
 of the old trunk, by the side of the first branch. 
 All these ramifications, as well as the oval body, 
 were pervious, although they would not admit 
 the common coarse injection. The old artery, 
 both before and beyond, was gradually con- 
 tracted towards the newly formed vessels, in a 
 greater degree than is expressed in the drawing. 
 Whether the branch H existed before the liga- 
 ture w'as made, I cannot determine. 
 
 The Ram of Experiment II., the left carotid 
 of which was tied on October 5th, 1814, so as 
 probably to cut through the cellular and fibrous 
 coats, and was again loosely tied with another 
 ligature, was killed on the 11th of September, 
 1815, and almost immediately injected from the 
 innominata. Here the injection ran w^eil on 
 the right side ; but on the left it failed, the 
 artery being' found to be, throughout, much 
 
 N 
 
178 A farther Power of Arteries. 
 
 contracted below its natural degree. For three 
 quarters of an inch, where the ligature had 
 apparently been applied, the trunk of the 
 artery was entirely lost; and in its stead were 
 two small cylinders, uniting the ends of the 
 pristine artery. One of these was, in some de- 
 gree, tortuous, and appeared to be hollow; having 
 in it some globules of blood, and communica- 
 ting with the cavity of the artery below, from 
 which it could be inflated with a blow-pipe. 
 Its cavity was, however, too small to receive the 
 coarse injection, which had stopped at its com- 
 mencement, but was found to have filled the 
 old part of the artery above, by some other 
 communication. The other cylinder, which 
 was attached to the former by a film of thin 
 cellular substance, was not found to be hollow. 
 
 These appearances in the two last sheep were 
 equally unexpected with those in the first ; 
 since it seemed a priori probable, that, as in 
 them the ligature was applied on one side only, 
 the corresponding artery would have transmit- 
 ted to the brain as much blood as was adequate 
 to all its purposes. 
 
 If, however, in these two instances, the re- 
 production of artery was less perfect than in 
 the first, we may reasonably attribute this dif- 
 
179 
 
 A farther Power of Arteries. 
 
 ference to the less degree of necessity which 
 arose out of the perviousness of the opposite 
 carotid. 
 
 Since, then, this peculiarity of structure 
 occurred in all the three cases of sheep, in which 
 the artery was, for a sufficient length of time, 
 exposed to the effects of the ligature, and was 
 never found in any of the much greater num- 
 ber of examples, in which the carotids had not 
 been so treated ; I think we may, with a degree 
 of probability amounting almost to certainty, 
 infer, that these accessory vessels were, in each 
 case, new formations, intended to compensate 
 the loss of the old artery, the functions of which 
 had been destroyed by the ligature. 
 
 It will, however, from the detail of our ex- 
 periments, have been seen, that l have now under 
 trial three other Rams, of which one has a liga- 
 ture on one carotid, and the two others on both. 
 Whatever results these experiments may afford 
 me, I propose to detail in an appendix to this 
 work. 
 
 In the mean while, it were greatly to be 
 wished, that similar trials might be made, by 
 others, on animals of various kinds ; and that the 
 gradations of change at different periods were 
 carefully examined, and faithfully recorded. 
 
180 A farther Power of Arteries. 
 
 The language of Haller ought to be that of 
 every physiologist. “ Des experiences reiterees 
 “ donnent un nouveau degree de force a ce que 
 “ les autres nous out appris; et je pouvois esperer 
 “ de decouvrir quelques v6rit6s, qui leurs 
 “ seroient echapp^es ; esperance fondee sur 
 “ une bonte, que je connois a la nature. On 
 “ ne la consulte jamais en vain ; et elle recom- 
 “ pense toujours les travaux de ceux, qui 
 “ 1’ etudient.” 
 
 FINIS. 
 
 Printed hy Richard Cruttwell, 
 St. James’s-Stree’. Rath 
 
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