312 Canadian Record of Science. 



not those of spontaneous rhythm, but as in part due to 

 excitation ; and for these reasons it seems to me my expes- 

 iments really indicate the amount of genuine spontaneous 

 rhythm of the heart of the Chelonians more nearly than 

 those of Gaskell, in which he has employed suspension, 

 recording levers, and feeding. 



At the same time I am inclined to believe that in the land 

 tortoise the ventricle has greater tendency to spontaneous 

 rhythm than in some other kinds of Chelonians. 



Since the part of the heart, not sinus proper and not con- 

 stituting the more prominent part of the auricles, is different 

 in appearance, in structure to some extent, and in function, 

 especially in its spontaneous rhythmic power, as well as 

 conductivity, &c, and inasmuch as it, in these respects, 

 approximates more closely to the sinus than to the auricle 

 proper, it would, I think, conduce to clearness, if this part 

 were considered and called the sinus extension. This seems 

 the more natural, seeing that a similar structure, nanifestly 

 more like the sinus than the auricle, exists in the fish.* 



Though this division was not clearly defined in my paper 

 on the Terrapin, "auricle" is used in the sense of the au- 

 ricle proper, or bulged part between sinus and ventricle. 



II. Reflex Cardiac Inhibition. 



The results of my experiments on this subject may be 

 shortly stated as follows : — 



1. Prolonged gentle tapping with a forceps over the ab- 

 dominal organs had less effect than a pushing down move- 

 ment with a seeker, and still less than a single sharp blow 

 with the forceps. 



2. Stimulation of the brachial plexus, with a strong in. 

 terrupted current, has not, in general, produced much slow- 

 ing of the rhythm. In one case it seemed to quicken it. 



3. Sponging over the peritoneum vigorously has general, 

 ly produced cardiac slowing or arrest. 



Peculiar Effects. — 1. In certain cases, electrical stimula- 



* " On the Structure and Rhythm of the Heart in Fishes," &c, 

 vol. vi. No. 4 and 5, Journal of Physiology. 



