490 Canadian Record of Science. 



After Effects of Vagus Stimulations. — These were of the 

 following kinds : — 



1. Increased rate of beat, more marked the slower the 

 heart at the time of stimulation, 



2. In all cases increased force (working power) of the 

 heart. This was, sometimes, the only effect noticeable. 



3. When irregularity of rhythm of either the whole or 

 some part of the heart existed prior to stimulation, this 

 was abolished for a longer or shorter period. 



In these respects the heart of the Snake follows those of 

 the other animals referred to above ; but none of the effects 

 have been so marked as in the case of the Chelonians, though 

 more certain than in the Fish, so far as my own observations 

 on that animal go. 



Mode of arrest and of re-commencement of the cardiac beat. — 

 When the current is too feeble to arrest the whole heart ; 

 or when the whole heart is not amenable to its action, as is 

 the case when its nutrition is much impaired, the auricles 

 are the first or only parts to stop pulsating. The sinus 

 venosus is always the first part to commence to pulsate 

 after vagus arrest, and for several beats the auricles proper 

 may be quiescent, the wave of contraction passing over 

 what I have called the " Sinus extension,'" to the ventricle 

 which may respond for some seconds prior to the auricles. 



I am inclined to believe that the auricles are not a little 

 dependent for the maintenance of their rhythm on the 

 intracardiac blood pressure, and that this may enter as one 

 factor into the explanation of this phenomenon. At all 

 events, the same takes place in all the poikilothermers I 

 have examined. McWilliam 2 pointed it out for the Eel, and 

 as I indicated in my paper on the Sea Turtle, 3 Gaskell 1 is in 

 error when he states that in the Tortoise an excitation wave 

 cannot travel from the sinus to the ventricle and cause a 



1 "The Ehythm and Innervation of the heart of the Sea Turtle," 

 Journal of Anat. and Phys., vol. xxi. 



2 Journal of Physiology, Vol. vi., Nos. 4 and 5. 



3 Op. cit. p. 7. 



1 Journal of Physiology, Vol. hi., Nos. 5 and 6. 



