The Heart of the Snake. 489 



On the Physiology of the Heart of the Snake. 



By T. Wesley Mills, M.A., M.D. 

 Professor of Physiology, McGill University, Montreal. 



This paper will furnish an account of a study of the 

 heart of the Snake, as a continuation of a series of papers 

 already published on the cardiac physiology of the cold- 

 blooded animals, including thus far also the Water Tortoise, 

 the Sea Turtle, the Fish, the Alligator, and Menobranchus. 



The snakes used belonged to the genus Tropidonatus, and 

 the experiments were made during the midwinter of 1886 

 and 188*7. The animals had been without food since their 

 capture in the autumn, but were not apparently in any 

 degree hibernating, the temperature of the apartment in 

 which they were kept being not far from 17° C. They were 

 left in a tank, with fresh water running constantly from a 

 tap, but they were free either to remain in the water or to 

 betake then elves to the dry shelves of the tank, on which 

 they were, in fact, mostly seen coiled up together. The 

 method of study has been that pursued throughout, viz., 

 direct observation, and as a stimulus, the interrupted current 

 supplied by a Du Bois' inductorium, fed by one good-sized 

 Daniell's cell. 



The Vagus Nerve. 



Comparison of the vagi througout these experiments has 

 established the following conclusions for this animal: — 



1. In no case was either vagus without effect on the 

 rhythm of the heart. In every case actual slowing, and 

 with a sufficiently strong current, arrest followed stimula- 

 tion. 



2. In the majority of instances the right vagus was more 

 efficient than the left. 



3. In a very few cases, both nerves seemed to be almost, 

 if not quite equally, influential over the heart's rate. 



In this comparison, then, it appears that the vagi of the 

 snake resemble functionally those of the other cold-blooded 

 animals examined by me. 

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