EXPERIMENTS AND OBSERVATIONS 
/ 
UPON THE 
CIRCULATION IN THE SNAPPING TURTLE, 
Clielonura Serpentina, 
WITH * 
ESPECIAL REFERENCE TO THE PRESSURE OF THE BLOOD 
IN THE ARTERIES AND VEINS. 
BY S. WEIR MITCHELL, M. D., 
LECTURER ON PHYSIOLOGY. 
PHILADELPHIA: 
PRINTED BY C. SHERMAN & SON. 
1862. ON THE 
CIRCULATION IN THE SNAPPING TURTLE. 
Since the experiments of Hales in 1731, and the later and more accurate researches of 
Poiseuille, a number of observers have studied the blood-pressures in various vertebrate 
animals, among which may be mentioned the horse, dog, sheep, cat, rabbit, and bird. 
So far as I can discover, the only observations of this nature upon cold-blooded vertebrata 
were made by Volkmann, who experimented upon frogs and fresh-water fishes. No other 
similar examination of blood-pressures appears to have been made, and up to the present 
date no one has studied the subject in connection with reptiles of any kind. 
The object of this memoir is to exhibit the results of a series of researches upon the 
blood-pressure in one of the most vigorous members of this class, the Chelonura serpen- 
tina, and thus to fill an important gap in our knowledge of heemometry. The reptile in 
question is admirably suited for this purpose. It is strong, active, singularly tenacious 
of life, and may be procured easily of any weight up to twenty-five or thirty pounds. 
Inhabiting the waters of many of the streams and mill-dams in the Middle States, it may 
be readily had in excellent condition during the spring and summer, and for all purposes 
of physiological and toxicological research, may be made use of whenever it is desirable 
to replace the frog by an animal of greater bulk and superior tenacity of life. 
The Snapping Turtles used in the following researches were brought from Havre de 
Grace on the Susquehanna river, and from the lower part of the State of Delaware, care 
being taken that only such were employed as had been captured by hand (dug out of the 
mud), rather than such as had been taken by the hook and line. 
As I have alluded to the great strength and tenacious vitality of these creatures, it may 
be well to make some brief statement of a more distinct nature as to the extent to which 
they are endowed with these qualities. 
A Snapper weighing twenty-seven and a half pounds was fastened by its tail to a ring, 4 
ON THE CIRCULATION IN 
and the blunt hook of a spring scale was caught in the upper jaw, the other end of the 
scale being also secured to the table. During this time the Turtle’s head was held extended. 
When it was released the animal drew it briskly into the cover of the shell, thus pulling 
on the scale until the index-point marked fifty-seven pounds as the force of the pull made 
by the retracted neck. Nearly equal vigor was manifested by others of the same species, 
and all were so active that by extending the head and using their powerful tails they were 
able to right themselves with ease, when placed on their backs, a position in which the 
Green Turtle becomes altogether powerless. 
The length of life in the separated head of the Snapper, and its power to bite long 
after being removed from the rest of the body, is very well known, but the astonishing 
resistance of the animal to one of our most active poisons is a still better test of its great 
and enduring vital power. So remarkable indeed was this, that I have studied it with 
some care, and described it at length in a separate paper. At present it will suffice to 
relate a single experiment illustrating the point in question. 
Assuming M. Bernard’s experiments* as a basis, if a Snapper weighing twenty-six pounds 
were a warm-blooded creature, it would be killed by the injection into its veins of about 
one-tenth of a grain of woorara. On several occasions I have injected into the jugular 
veins of Turtles weighing from twenty to twenty-seven pounds, thirty times this amount. 
The animal became motionless within five minutes, but soon began to recover, and at the 
close of twenty-four hours was, in several instances, as well as ever. As the heart’s action 
is not primarily checked by this poison, which acts only on the motor nerves, it is gradu- 
ally eliminated, and after some hours the power to move the respiratory muscles returning, 
the Turtle gradually recovers all its usual activity; the limit of endurance being the 
length of time during which the reptile can exist without renewing its supply of oxygen. 
I have occasionally seen Turtles weighing two or three pounds, so poisoned with woorara 
as to remain motionless and without the least reflex movement during three days, after 
which life and action gradually but completely returned. 
It will thus be seen that for strength and tenacity of life, the Snapper is well suited to 
exhibit a type of reptilian blood-pressures. 
The following points were made the subjects of study: 
1st. The arterial pressure. 
2d. The force of the heart’s contraction. 
3d. The effect of inspiration and expiration on the arterial pressure. 
4th. The influence of muscular motion on the arterial blood-pressure. 
5th. The blood-pressure in the central and distal ends of divided veins. 
6th. The effect of muscular exertion on the venous pressures. 
* Sur les substances toxiques, etc. Paris, 1857, p. 335. THE SNAPPING TURTLE. 
5 
The instrument used in the following experiments was the hsemometer of Magendie, 
as modified by M. Bernard.# The blood was kept fluid by filling the caoutchouc tube of 
the instrument with a saturated solution of carbonate of soda, which was found to displace 
two millimetres of mercury in the registering tube. Accordingly a reduction to this 
extent from the record of blood-pressure has been made in each instance. Any further 
description of an instrument so well known to physiologists would be altogether unne- 
cessary. 
Experiment.—Turtle weighing twenty-two pounds, from Delaware. Temperature of 
air 73° F. Present, Messrs. Keene, Stone, and Cantrell. The Turtle having been pro- 
perly secured so as not to impede the circulation or respiration, a tube was placed in the 
left femoral artery and connected with the caoutchouc tubef of the luemometer, when the 
following record was obtained after a few minutes’ repose: 
TIME. 
PRESSURE. 
REMARKS. 
Minimum. 
Maximum. 
4.41 p. M. 
30 M.M. 
40 M.M. 
Pulse 28 to the minute. 
4.42 
35 
45 
Respiratory act. 
4.44 
33 
43 
4.46 
33 
45 
Slight respiration. 
4.47 
30 
38 
4.49 
36 
43 
Respiratory act. 
4.50$ 
32 
40 
4.52* 
27 
37 
After respiration. 
4.53 
33 
42 
Cleaned tube, no clot in it. 
4.56 
29 
38 
4.57 
28 
37 
When violent movements took place, during whicn ine 
pulse became too irregular for notation. The ex- 
tremes reached, were 
23 
49 
4.57$ 
26 
35 
No clot in tube. 
4.58 
27 
37 
28 
3 7 
25 
98 
30 
40 
A full respiratory act. 
5.6 
28 
37 
After respiratory act. 
30 
42 
« - 
5.12 to | 
27 
37 
5.15 } 
29 
37 
Pulse 28. During respiration and violent motion, 
the limits were 
29 
43 
During several minutes, 
29 
36 
Steady pulse. 
June 18th, 1861. Present, Messrs. Keene, Stone, and Cantrell. 
Experiment No. 2.—Temperature 71° F. Snapping Turtle. Weight twenty-two 
* Legons sur les Proprietes Physiologiques et lcs Alterations Pathologiques des Liquides de l’Organism, par 
M. Cl. Bernard.—T. I, p. 167. Paris, 1859. 
f This tube was so thick as to withstand perfectly the dilating force thus brought against it. 6 
ON THE CIRCULATION IN 
pounds. The left carotid artery was isolated without loss of blood, a tube secured in the 
opening, and the following record obtained: 
TIME. 
PRESSURE. 
REMARKS. 
Minimum. 
Maximum. 
6.3} 
37 M.M. 
47 M.M. 
6.6 
35 
44 
6.6} 
35 
44 
6.10 
35 
44 
6.11 
36 
47 
Respiratory act. 
6.18 
32 
38 
6.18} 
30 
37 
6.26 
33 
41 
Tube cleaned. Minute loose clot in artery. 
6.29 
36 
46 
6.29} 
41 
53 
Respiratory act. 
6.32} 
36 
46 
49 
59 
After violent movement and repeated respiration, 
32 
43 
Steady and regular. 
The above observations are given in full, as an example of the mode of conducting the 
experiments. In every case, the extreme pressures were noted; but no complete record 
was kept of the influence of every respiratory act or muscular movement. Very little 
trouble was given by the clotting of the blood in the vessel or tubes, and even when 
clots did form, they were so loose in texture as scarcely to interfere with the registration 
of pressure. 
In the experiments of Poiseuille, Volkmann, and Vierordt, the mean between the ex- 
tremes of the rise and fall was given as the standard of arterial blood-pressure, and the 
instrument used was some form of Poiseuille’s htemadynamometer. M. Bernard has since 
shown that the haemometer of Magendie, which he terms the cardiometer, is a better 
instrument for exhibiting the changes of circulation with rapidity and exactness, and that, 
moreover, its registration gives higher numbers for the pressures than the older instru- 
ment. Having made use of the same apparatus in my own researches, 1 have preferred 
to follow M. Bernard’s method of notation, which may be easily explained in a few 
sentences. 
This distinguished observer states that when the cardiometer is connected with the 
artery of an animal the mercury rises to a varying height, which he calls the arterial 
pressure, believing it to be due, in part at least, to the elasticity and vital contractility 
of the arterial walls. Each pulse of the heart elevates the column of mercury to a 
certain point above this, whence again it falls during the diastole of the ventricles. The 
excess of mercury thus lifted he takes to represent the power of the heart’s systole. Both 
of the numbers thus obtained may vary with the individual and with the respiratory and 
other movements of the body. M. Bernard holds the view that the arterial tension is 
not due alone to the injecting power of the heart, and that certain agents, which alter the 
heart-force, do not diminish the arterial tension, whilst other substances which plainb THE SNAPPING TURTLE. 
7 
lessen the arterial tension, do not alter the power of the central propelling organ. Most 
physiologists are of opinion that the intersystolic pressure is indirectly, but alone due to 
the action of the heart, the arteries only restoring to the blood, so to speak, the excess of 
power employed in their distension, during the. contraction of the cardiac pump. Thus, 
if in the case of a warm-blooded mammal, the mercury of the manometer should rise to 
100 m.m., and at each heart-pulse leap to 120 m.m., falling during the diastole again to 
100 m.m., M. Bernard would describe the arterial pressure as represented by the weight 
of a column of mercury of a 100 m.m., and would estimate the heart-force at 20 m.m., 
M. Poiseuille, on the other hand, would give the average, or 110 m.m., as representing 
the circulatory pressure. 
Further research is needed before this question can be settled, and as the difference is 
merely one of mode of statement, I have preferred to follow M. Bernard’s method of 
notation, without feeling pledged to the correctness of the views upon which its practice 
is founded. 
The following results were obtained from observation of the pressure of the blood in 
the carotid arteries of eight Snapping Turtles, every possible precaution being taken to 
prevent loss of blood or injury to nerves and veins while insulating the artery. The 
numbers here given are those which were noted when the Turtle was in repose and not 
breathing. As the respiratory acts occurred at intervals of from one to three minutes, 
observations were easily obtained during these periods of repose. 
No. 1. Snapping Turtle. Weight 23 lbs. Temp, of air 71° F. Pulse 25. The 
tube was placed in the left carotid: 
MINIMUM. 
MAXIMUM. 
DIFFERENCE. 
35 M.M. 
45 M.M. 
10 M.M. 
35 
44 
9 
35 
44 
9 
32 
38 
6 
30 
37 
7 
32 
43 
11 
Mean, 33.2 
41.8 
8.6 
No. 2. Snapping Turtle. Weight 20 lbs. Temp. 72° F. Pulse 29. The tube was 
placed in the left carotid: 
MINIMUM. 
MAXIMUM. 
DIFFERENCE. 
39 M.M. 
48 M.M. 
9 M.M. 
41 
53 
12 
41 
53 
12 
38 
47 
9 
39 
47 
8 
39 
50 
11 
33 
47 
14 
37 
44 
7 
Mean, 38.4 
48.6 
10 2 8 
ON THE CIRCULATION IN 
No. 3. Snapping Turtle. Weight 261 lbs. Temp, of air 76° F. Pulse 31. The 
tube was placed in the left carotid: 
MINIMUM. 
MAXIMUM. 
DIFFERENCE. 
29 M.M. 
42 M.M. 
13 M.M. 
29 
43 
14 
29 
38 
9 
28 
38 
10 
26 
37 
11 
22 
33 
11 
20 
30 
10 
24 
34 
10 
23 
32 
9 
29 
39 
10 
24 
34 
10 
Mean, 25.7 
36.3 
10.6 
No. 4. Snapping Turtle. Weight 241 lbs. Temp, of air 72° F. Pulse 27. The 
tube was placed in the left carotid: 
MINIMUM. 
MAXIMUM. 
DIFFERENCE. 
33 M.M. 
49 M.M. 
16 M.M. 
34 
51 
17 
33 
49 
16 
31 
46 
15 
30 
47 
17 
33 
51 
18 
31 
46 
15 
34 
47 
13 
33 
45 
12 
34 
47 Pulse 32. 
13 
33- 
43 
10 
Mean, 32.6 
47.3 
14.7 
No. 5. Snapping Turtle. Weight 21 lbs. Temp, of air 77° F. Pulse 40. A tube 
was placed in the left carotid: 
MINIMUM. 
MAXIMUM. 
DIFFERENCE. 
34 M.M. 
47 M.M. 
13 M.M. 
33 
50 
17 
42 
58 
16 
36 
49 
13 
37 
49 
12 
41 
53 
12 
42 
51 
9 
37 
51 
14 
Mean, 37.7 
51 
13.3 
No. 6. Snapping Turtle. Weight 20 lbs. Temp. 79° F. Pulse 36. The tube was 
placed in the left carotid: THE SNAPPING TURTLE. 
9 
MINIMUM. 
MAXIMUM. 
DIFFERENCE 
40 M M. 
56 M.M. 
16 M.M, 
37 
50 
13 
37 
50 
13 
37 
52 
15 
37 
52 
15 
Mean, 37.6 
52 
14.4 
No. 7. Snapping Turtle. Weight 191 lbs. Temp, of air 74° F. Pulse 30. The 
tube was placed in the left carotid: 
MINIMUM. 
MAXIMUM. 
DIFFERENCE 
30 M.M. 
39 M.M. 
9 M.M. 
36 
47 
11 
29 
40 
11 
31 
41 
10 
31 
41 
10 
32 
43 
11 
Mean, 31.5 
41.8 
10.3 
No. 8. Snapping Turtle. Weight 191 lbs. Temp, of air 74° F. Pulse 30. The 
tube was placed in the left carotid: 
MINIMUM. 
MAXIMUM. 
DIFFERENCE 
39 M.M. 
45 M.M. 
G M.M. 
39 
44 
5 
35 
45 
10 
30 
41 
11 
30 
39 
9 
35 
44 
9 
31 
40 
9 
Mean, 34.1 
42.5 
8.4 
Upon comparing the above records, it will be seen that the mean of the minimum 
pressures is 33.8; that of the maximum 45.1; and that of the difference 11.3. The first 
number, therefore, represents the average height of a column of mercury sustained by the 
arteries during the diastole of the heart, the average effect of the systole being to lift the 
column 11.3 m.m. higher. The statements in regard to the blood-pressures in mammals 
vary so much that it is not easy to find a standard of comparison with those of chelonians; 
but, assuming M. Bernard’s observations to be correct, we find that the minimum of pres- 
sure in the arteries is nearly the same in mammals of all sizes, being about 
110 m.m, in the horse. 
103 m.m. in the dog. 
95 m.m. in the rabbit. 
The rise caused by the heart-beat bears, however, a greater relation to the size of the 
animal, and is noted in the above animals as 65, 12, and 5 respectively. The minimum 
pressure in the artery of the Snapping Turtle is, therefore, about one-third that in the 10 
ON THE CIRCULATION IN 
artery of a mammal, or as 33.3 to 110, 103 or 95, according to the animal chosen for 
comparison. 
The force of the heart-act in the Turtle elevates the column, on an average, 11 m.m., 
which is about the pressure observed in a dog of middle size when tranquil, and when the 
respirations do not prevent accurate observation of the influence of single pulsations, as 
is commonly the case. 
Upon reviewing these results, it is hardly possible to escape the conviction that the 
capillary circulation must for some reason be more easily carried on in the Turtle, or else 
that in this animal the arteries are more relaxed than in the dog for example, and less 
contractile than in mammals of like weight. In cold-blooded vertebrates, such as the 
frog and fresh-water fish, M. Volkmann* found the arterial pressures to vary between 18 
m.m. and 84 m.m. 
The impulse conveyed to the column of blood during the systole of the heart in the 
Turtle is somewhat different from that of the mammal. In place of a sudden and abrupt 
motion, as seen in these latter animals, the mercury moves so slowly that the time of its 
rise during a systole may be estimated at one second, the period of fall being one second 
and one-fifth. The rise of the mercury was usually steady and regular; its fall was 
broken and irregular, so that after falling two-thirds of the distance rapidly, an equal 
time was occupied in effecting the remaining third of the total descent. The number 
of heart-pulsations varied in the eight animals examined from 25 to 40. In the individual 
cases its number was scarcely altered during the whole observation. 
The same regularity did not prevail in the circulating current, and, apart from the influ- 
ence of respiration and muscular motion, it may be seen that the pressure varied from 
time to time, owing to causes which I was unable to understand. 
EFFECT OF INSPIRATION, EXPIRATION, AND MUSCULAR MOTION ON THE ARTERIAL PRESSURES. 
Before considering these points it will be proper to make a brief statement as to the 
mechanism of the respiration in the Snapper. All of the leading authorities on the 
physiology of chelonian reptiles describe their respiration as effected by an act of deglu- 
tition similar to that which occurs in the batrachia.'f* However this may be in some clie- 
lonians, I have arrived at the conclusion that in the Snapper the respiratory movements 
are entirely effected by abdominal or thoracic organs, and that their type is that of the 
mammal rather than that of batrachians. If, for example, the Turtle’s mouth remains 
open it breathes as usual, which would be impossible were its respiration effected by an 
action of swallowing the air or of forcing it into the lung, according to the usual 
statement. 
* Yolkmann. Die Hamodynauiick. 
f Milne Edwards. Legons sur le Physiologie, etc., Paris, 1858. Tome II., 2d partie, p. 387. THE SNAPPING TURTLE. 
11 
To settle the question more completely I cut the trachea of a Snapper across, and still 
found that the breathing went on at the ordinary rate. Next, a bent glass tube, two 
millimetres in width, was adapted to the upper end of the divided trachea and allowed to 
dip into water. The water rose and fell in the tube about one millimetre only at each 
respiratory motion, and even this was clearly due to the synchronous reflex movements in 
the laryngeal muscles, which open and shut the glottis during the act of breathing,—a 
circumstance which is also observed to take place in higher vertebrates, as Dr. Dalton has 
well shown. 
Lastly, the bent tube was adapted to the lower end of the divided trachea and again 
dipped in water. At each inspiration the fluid was largely drawn up into the lung and 
rejected again during the subsequent expiration. It is, therefore, impossible to concede 
that this type of respiration is any other than that which is seen in mammals, and we 
must admit at once that the whole respiratory movement is effected in the Snapper as in 
them by the agency of thoracic and abdominal groups of muscles. 
I have, elsewhere, shown more fully the mode in which they effect this end and the 
part played by the various muscles thus employed. 
liespiration occurs in the Snapper about once in a minute in some cases, and often less, 
as once in two or two and a half minutes in others, while this animal undoubtedly has 
the power to exist a long time without breathing, when the process would involve incon- 
venience. 
The respiratory process consists first of a full expiration, which is followed at once by 
a long and very large inspiration, and that again by a short and incomplete expiration, 
which still leaves the lungs more or less full until the time for the next respiratory move- 
ment arrives, when again a long expiratory act begins it. 
During the interval between two respiratory acts, a slight pulsatile motion is visible in 
the space between the two limbs and the carapax and plastron. This movement appeared 
to be respiratory in its character, and to test the correctness of this view I resorted to the 
following plan. 
Experiment.—A large tube was placed in the lower end of the divided trachea, and a 
smaller glass tube* fitted to it and bent at an angle of 45 degrees. The open end was 
allowed to rest in water. In the intervals between the full respirations above described, 
the water rose and fell in the tube about 3 to 4 m.m., and this movement corresponded 
with the motion observed on the flanks of the animal. It was, however, so small in 
amount, the tube being only 2 m.m. in width, that it could scarcely be said to effect any 
change of moment in the mass of air in the lungs, and at the utmost could only be 
efficient in shifting slightly the air in contact with the various parts of the breathing 
* 2 millimetres wide. 12 
ON THE CIRCULATION IN 
surfaces. A very simple experiment finally decided the nature of the motion above 
described. 
Experiment.—A tube having been placed in the right carotid artery was connected with 
the luemometer. A second tube, fitted to the cut trachea, was so bent as to be allowed 
to dip just below the surface of a vase of water. On bringing the arterial and tracheal 
tubes near together, the rise and fall of the fluids in both was found to be exactly syn- 
chronous. The pulsatile motion perceived in the flanks and transmitted through the 
lungs, as shown above, seems, therefore, to be due to the propagated impulses from the 
neighboring vessels, and, perhaps, in part also from the pulmonary arteries. 
During the interval between two respirations the column in the luemometer tube rose 
and fell with singular steadiness at times. The long expiration which begins the series 
of respiratory motions, had no marked effect on the column sustained. The long inspi- 
ration which followed caused a small rise in the mercury, and the short incomplete expi- 
ration which terminated the series of movements raised it still higher. 
The following experiment will serve to exemplify the amount and character of this 
influence. 
Snapper. Weight 19£ lbs. Temp. 70° F. Pulse 33. Tube in the left carotid: 
TIME. 
MINIMUM. 
MAXIMUM. 
DIFFERENCE. 
RESPIRATORY STATE. 
4.10 P. M. 
34 M.M. 
45 M.M. 
11 M.M. 
4.12 
34 
44 
10 
Expiration. 
36 
46 
10 
Inspiration. 
40 
51 
11 
Short expiration. 
4.14* 
33 
40 
7 
Expiration. 
33 
41 
8 
Inspiration. 
39 
49 
10 
Short expiration. 
In mammals it is easy to see why active expiration should cause an increased pressure 
in the arteries, since the thorax is contracted and the belly drawn in so as to exert con- 
siderable compression upon the large arteries, and thus to cause an instant rise in the 
manometric column of mercury attached to an artery. In the Turtle the first respiratory 
act is a slow one, and the amount of force employed in effecting it but small; whence no 
marked influence is visible in the arteries. The long inspiration which follows usually 
increases a little the arterial pressure, although sometimes, where the action of breathing 
is not energetic, no such effect can be seen. The cause of the slightly increased pressure 
alluded to above I have been unable to fathom. The short expiration which completes 
the respiratory series at once raises the arterial pressure. This is, probably, due to the 
fact that at this time the lung distended with air is favorably situated to exert direct 
pressure on neighboring vessels, and also to the fact that this final expiratory motion is 
vigorous and abrupt. THE SNAPPING TURTLE. 
13 
The effect of muscular movement upon the pressure of the blood in the arteries was 
well marked and interesting. During violent movement the force of the heart remained 
unaltered, but the whole column of mercury rose, a result which attained to a maximum 
when the movements were coincident with the long inspiration and the short expiration 
which terminate each single series of respiratory movements. On such occasions the 
mercury sometimes rose as high as 70 m.m. and the action of the heart was irregular 
and unequal in force. Immediately after the movements were over, the mercurial column 
fell to a much lower point than usual, and then gradually ascended to the normal stan- 
dard, as illustrated by the following record. 
Experiment.—Snapper. Weight 241 lbs. Temp, of air 78° F. Tube in left carotid. 
Not all the respiratory acts were here noted: 
TIME. 
MINIMUM. 
MAXIMUM. 
4.45 
33 M.M. 
49 M.M. 
4.47 
34 
51 
4.48 
33 
49 
20 
50 
During violent struggles the heart acting irregu- 
larly. 
4.55 
31 
46 
Pulse 27. 
5.06 
33 
51 
Free movement. 
5.11 
31 
46 
5.13 
15 
70 
Prolonged movements and active respirations, 
during which this rise took place. 
31 
46 
5.21 
34 
47 
Movement. 
5.27 
27 
33 
5.28 
31 
40 
Movement very violent. 
5.29 
10 
18 
5.34 
32 
44 
5.34} 
33 
45 
Pulse 28. 
VENOUS BLOOD-PRESSURES. 
The arrangement of the veins of the neck in the Snapper favor peculiarly an exami- 
nation of the blood-pressures, since they are so large and numerous that an interruption 
of the current in one of them does not at all interfere with the general flow of blood 
towards the heart. 
Both carotids are accompanied by one large internal jugular vein, and sometimes by 
two. The external jugular is also very large, and the oesophagus is surrounded by a 
plexus of anastomosing veins of large dimensions. At the back of the neck there are 
also one or two dorsal veins of considerable size. 
Experiment.—Turtle. Weight 20 lbs. The tube was placed in the distal end of the 
internal jugular vein, when the mercury rose to 6 m.m. and was seen to pulsate feebly, the 
column rising about I m.m. at each heart-pulse. Violent motion raised the column to 11 14 
ON THE CIRCULATION IN THE SNAPPING TURTLE. 
m.m. in one case and to 14 m.m. in another. Pulse 29. The carotid artery at this time 
exhibited a pressure of from 41 to 53 m.m. 
Experiment.—Turtle. Weight 20 lbs. The tube having been placed in the distal end 
of the vessel, the column rose to 5 m.m. Slight pulsation of £ to i m.m. During mus- 
cular action it rose to 28 m.m. Pulse 36. The tube was next placed in the cardiac end 
of the cut vein, when it rose to 3 m.m. and pulsated about 1 £ m.m. Similar results were 
obtained upon further experiment. When the tube was placed in the distal end of a 
large vein, the average height of column of mercury supported was 6.7 m.m. In the 
cardiac end of the same veins the average was 3 m.m. In all cases muscular motion 
elevated the column from 11 to 30 m.m. 
It will be seen above that a pulsation of feeble character took place even when the 
distal end of the vein was examined. This singular phenomenon appears to be a normal 
occurrence in the larger veins of the neck. In those of the limbs it was scarcely per- 
ceptible, but in the neck it was always visible, and was well marked in the great veins, 
and best of all in the external jugular. At first I supposed it to be due to the pulsation 
of neighboring arteries, or to the transmission through anastomotic channels of the pulse 
which is noticed when the lower or cardiac end of a vein is the subject of study. The 
first of these possibilities is negatived by the fact that the pulsation was still seen where 
the vein chosen was remote from any large artery, which is the case with the external 
jugular vein. The second is disposed of by making use of the dorsal vein or external 
jugular far up in the neck, and where it is thus remote from large communicating 
branches. 
The pulsation referred to is, in all probability, due to the propagation of the heart-force 
through the capillary system into the veins. The venous pulse which was observed in the 
cardiac end of the veins of the neck, was not visible in the veins of the limbs. It was 
due, no doubt, to the pulsatile action of the walls of the vena cava, so well described 
by Alison. 
Muscular movements, as in other animals, increased the venous pressure considerably. 
The influence of the respiratory acts on the venous circulation was imperfectly studied, 
owing to a failure of proper material, and is, therefore, reserved for future study.