The Heart of the Sea-Turtle. 313 



tion of the anus has caused marked arrest of the heart; hut 

 in others, a preliminary slowing, followed by an accelerated 

 rhythm, while the current is still passing. 



2. In certain cases, stimulation of the liver has led to the 

 usual cardiac arrest ; but in others, acceleration has been 

 the first result and the only one ; while in still others, accele" 

 ration has followed and preceded slowing. 



It is to be understood that, in all these cases, the spinal 

 cord and medulla oblongata were intact. 



The significance of such results as those cited aboved are 

 discussed in my paper on the Alligator.* 



Upon the whole, it may be said that, while in the matter 

 of cardiac arrest by reflex agency, there is much similarity 

 among the different genera and species of Chelonians, the 

 Chelonia mydas is the most susceptible of the three species 

 examined by me ; and the Slider Terrapin, is almost if not 

 quite equal to it in this respect, and in advance of the other 

 marine turtles. The condition of the animal at the time of 

 experiment is also a most important factor. 



III. Stimulation of the Vagi. 



The possible effects of stimulation of the vagi in the ma- 

 rine turtles are : — 



1. Preliminary weakening of the beat, most marked in 

 the auricles, without arrest of the heart's action or change 

 in the rate of beat. This may occur with a very weak cur- 

 rent ; but more frequent is — 



2. Arrest of the auricles ; the rest of the heart continuing 

 either with unchanged or a slowed rhythm and weakened 

 beat. G-askellf has stated in "his paper on Testudo Grceco 

 that he had never seen any evidence that an excitation wave 

 is able to travel from the sinus to the ventricle and cause a 

 ventricular contraction independently of a wave of con- 

 traction over both parts of the auricle. The latter state- 

 ment is at variance with my observations on the Terrapin 

 and still more frequently on the marine turtles. Often, 

 when both auricles proper are arrested by stimulation of 



* Journal of Anat. and Phys., vol. xx. • 



f Journal of Physiology, vol. iii. Nos. 5 and 6. 



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