a 
226 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.t However this may be in some che- 
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. 
* Volkmann. Die Hamodynamick. 
+ Milne Edwards. TLecons sur Je Physiologie, ete., Paris, 1858. Tome II., 2d partie, p. 387. 
