Physiology of the Heart. 101 



examined, the ventricle has in most cases a certain capacity 

 for independent rhythm, but that apart from all forms of 

 stimulation, this rhythm is never very marked, though it may 

 last for hours. This seems to be greater in the land tortoises 

 than in other Chelonians. 



The ventricle of the sea turtle is characterized by great 

 sensitiveness as compared with that of other Chelonians, 

 hence its spontaneous rhythm may be greatly increased 

 by slight stimulation. Results, like those of Gaskell, 

 obtained by suspending the heart, attaching recording 

 levers and feeding it through its own system of 

 vessels, without regard to the normal blood pressure 

 therein, must not be considered as those of pure spon- 

 taneous rhythm, for such methods furnish stimulation. 

 In my experiments, the heart was kept surrounded with 

 nutriment and covered so as to provide a "moist chamber," 

 but it remained in situ. The ventricle was separated by 

 ligature in most cases, by section in a very few. 



Is there a Depressor Nerve in the Chelonions ? — Blood pres- 

 sure experiments on the terrapin and the sea turtle have 

 shown that no nerve, with the characters of a physiological 

 depressor, exists in this family. Certain fine nerves in the 

 neck of the sea turtle have, on stimulation, given results of a 

 peculiar and puzzling kind. They have been inconstant in 

 action, sometimes giving rise to acceleration, sometimes to 

 retardation of the cardiac rhythm, or to both — now one, and 

 now the other. 



Stimulation of the Cerebral End of one Vagus, the medulla 

 and other vagus being intact in all the Chelonians I have 

 examined, has usually produced cardiac arrest. In the sea 

 turtle, in one case, this was followed by decided after- 

 acceleration, but the different genera of Chelonians and 

 even different species and individuals show variation in this 

 respect, as also in the degree to which the heart can be re- 

 flexly inhibited ; the terrapin and 0. Midas resembling each 

 other most and giving the best marked results. In fact this 

 research has confirmed the truth of the law, that with ana- 

 tomical resemblances are usually associated physiological 

 ones. 



