The Heart of the Sea-Turtle. 311 



in the ventricle. C. mydas has shown much the greatest 

 capacity for spontaneous cardiac rhythm of the species of 

 marine turtles examined by me. 



3. The spontaneous rhythm of the ventricle never equals 

 that of the original rhythm of the ventricle, in fact, usually 

 remains very slow indeed. 



An examination of the cases reported from my exper- 

 iments above will show that the ventricle has a purely 

 spontaneous rhythmic tendency, but that this tendency is 

 after all rather feeble. 



In all the experiments, the heart was left in situ, sur- 

 rounded either by pericardial fluid, blood plasma, or serum, 

 so that its nutrition was provided for. 



When ligatures were used, a certain quantity of blood was 

 imprisoned necessarily within the cavities thus shut off. 



A glass vessel was also placed over the heart, thus forming 

 a moist chamber. 



The heart of the marine turtle is much more sensitive to 

 conditions of nutrition than that of either the land tortoise 

 or the Terrapin, which is, of course, an obstacle in the way 

 of the development of spontaneous rhythm. 



I have found that unless the ligatures used are somewhat 

 fine and drawn very tight, a rhythm may arise possibly not 

 equal to the original one, nor to that of the part of the heart 

 usually dominating the rhythm in question {e.g., auricle the 

 ventricle), thus imitating a genuine spontaneous rhythm ; 

 while in reality it is in part due to stimulation from the 

 wave of contraction of the part above, the ligature causing 

 a sort of marked "block" only. 



With so sensitive a ventricle as that of the marine turtle, 

 I am satisfied the attachment of a lever and the effects of 

 the same on the rhythm would be considerable. If feeding 

 the heart could be so regulated that the pressure within its 

 own special arterial system did not exceed the normal, it 

 might be unobjectionable ; but it is difficult or impossible 

 to ascertain what this norme is. I therefore regard results 

 obtained with the attachment to the heart of a recording 

 lever, suspension of the heart and feeding it through its 

 own vesselsj except under the conditions defined above, as 



