Experiments and observations upon the circulation in the snapping turtle, Chelonura serpentina : with especial reference to the pressure of the blood in the arteries and veins / by S. Weir Mitchell.
- Silas Weir Mitchell
- Date:
- 1862
Licence: Public Domain Mark
Credit: Experiments and observations upon the circulation in the snapping turtle, Chelonura serpentina : with especial reference to the pressure of the blood in the arteries and veins / by S. Weir Mitchell. Source: Wellcome Collection.
Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)
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![In mi: < [RCULA1I0N IN rj of a mammal, oi u 33.3 to 110, 103 or 95, according to the animal chosen for i omparison. The force of the heart-ad 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 ( ommonl] the case. Upon reviewing these results, it is hardly possible to (-scape the conviction that the capillary circulation must for seme 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 ;u1(l fresh-water fish, M. Volkmann* found the arterial pressures to vary between IS m.m. and S4 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-tilth. 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 \ oBmmdil Die Bamodjnatnick.](https://iiif.wellcomecollection.org/image/b21141617_0010.jp2/full/800%2C/0/default.jpg)
