138 Canadian Record of Science. 



been published on the heart physiology of this group of 

 animals. 



The work of the present writer, while it confirms Gaskell's 

 conclusions as regards the cardiac accelerator, is wholly at 

 variance with his views as to the functions of the vagus. The 

 vagus in the Crocodilia, at least in the alligator, is not a pure 

 cardial depressor, but is on the contrary a powerful cardiac 

 augmentor. 



The result of the stimulation of the vagus may be thus 

 stated : 



(1.) Stimulation of the vagus with a weak, interrupted 

 current may weaken the cardiac beat with or without arrest 

 of the auricles ; the latter may be arrested and give rise to 

 a brief stop of the ventricles. 



(2.) "With a stronger current, the sinus may be so weak- 

 ened as to lead to arrest of the auricles and ventricles ; 

 or the sinus may be arrested wholly, in which case the 

 auricles and ventricles invariably cease to beat. 



(3.) When the cardiac beat recommences, it may be in the 

 order, sinus, sinus extension, ventricles ; or sinus, auricles, 

 s. extension, ventricles, i. e., the auricles may remain 

 quiescent as in the Chelonians and fishes when all the rest of 

 the heart is beating. 



(4.) The rhythm after vagus stand -still may be (a) without 

 acceleration, or (b) accelerated. 



The augmentation in the force of the beat is more marked 

 than acceleration in the rate. Both rate and force follow, 

 as in the Chelonians, the law of inverse proportion. 



Comparison of the Vagi and Results of their Prolonged Alter- 

 nate Stimulation. The vagi in the alligator, as in the Che- 

 lonians, have not, as a rule, equal power in causing and 

 maintaining cardiac inhibition ; the right, as in the other cold 

 blooded animals examined, being more effective. Prolonged 

 stimulation of the vagi alternately leads to corresponding 

 lengthened cardiac arrest. 



Accessory Vagi. Certain small nerves are in the alligator 

 given off from the Glossopharyngeal shortty after its exit 

 from the skull, proceed downwards, apart from the vagus, 

 and pass beneath the trachea over the vessels to the heart. 



