310 Canadian Record of Science. 



finger suffices to start the ventricle into a rhythm of 24, lasting for 

 two minutes. 



This latter observation illustrates well the great sensitiveness or 

 excitability of the ventricle of the sea-turtle. 



Exp. VI. — Chelonia my das ; animal bled to death; after destruc- 

 tion of brain. 



1.30 p.m. Cut away sinus from auricles, sinus extension, and 

 ventricle; very soon a rhythm arises in the latter parts. 



2.10 p.m. Eight auricle beats slightly before the left. 



2.40 p m. Left auricle beats only feebly ; ventricle getting rigid. 



3.10 p.m. Ventricle wholly rigid ; right auricle beating at rate of 

 12 : left auricle quiescent ; vertical section made between the au- 

 ricles, &c. ; right auricle continues to beat. 



Exp. VII. — Chelonia imbricata. 



10 a-m. Cut away side ventricle from rest of heart ; then the au- 

 ricles proper from the sinus extension and the ventricle free from 

 the parts above it. This gives rise in the ventricle to a rapid rhythm 

 of excitation for a very short time, followed by a rhythm of 1-2 in 

 the minute for 3-4 minutes ; rhythm of heart at time of section, 20. 



10.15 a.m. Sinus extension a rhythm of 19, and irregular. 



10.30 a.m. " " 13. 



10.45 a.m. " " 12. 



Ventricles no pulsation throughout. 



12 noon. Ventricle rigid ; sinus extension a rhythm of 15, and 

 irregular ; auricles proper die much later than ventricles, but have 

 no spontaneous rhythm whatever. 



This experiment clearly demonstrates the greater tenden- 

 cy to, and capacity for, spontaneous rhythm of the sinus 

 extension (or " basal " or flattened portion of the auricle) 

 than any other part, including the auricles proper. 



To state the results of the rest of my experiments would 

 be very much of a repetition of the above ; the experiments 

 have been numerous and occupied much time, and justify, 

 I think, the following conclusions for the sea-turtle : — 



1. The power of originating spontaneous rhythm is in the 

 order : sinus, sinus extension, auricle, ventricle ; that of the 

 sinus being much the best marked. 



2. The degree of spontaneous rhythm of the ventricle 

 varies with the species (and individual) and the state of 

 nutrition and general vitality of the animal. This probably 

 applies also to the rest of the heart, but is most conspicuous 



