322 Canadian Record of Science. 



less successfully, as the sea-turtle has less vital tenacity than 

 other genera of this family ; indeed, there often seems to be 

 associated great vital tenacity of the animal with ;a corres- 

 ponding resisting power of the heart, as evinced in the case 

 of Batrachus tau, the fish on which my experiments were 

 chiefly made. 



YI. Nerves with Peculiar and Inconstant Influence. 



Reference is made in my earliest communication on the 

 Chelonians* to a fine nerve which on the first stimulation 

 produced cardiac arrest followed by acceleration, but the 

 later stimulation of which seemed to be without effect on 

 the rythm. 



I have described what seemed to be accessory vagi in the 

 Alligator. 



In the sea-turtle, I have met with fine nerves traceable 

 upwards towards the superior cervical ganglion and down- 

 wards to the heart, which have acted in a somewhat incon- 

 stant manner. Thus sometimes such a nerve has given 

 purely vagus effects ; again, a first stimulation has caused 

 slowing, and all later stimulations only acceleration ; while 

 others again have shown no action beyond the first one, on 

 repeated stimulation. But this I have also noticed to hold 

 for the small accelerating branch from the middle cervical 

 ganglion in the Terrapin. Of course, such fine nerves die 

 readily, and are easily exhausted by stimulation , and it 

 may be that the inhibitory fibres in some cases are fewer 

 and are exhausted sooner than the accelerating ones : how- 

 ever, such phenomena, in the present state of our know- 

 ledge, are rather puzzling. 



Is there a Physiological Depressor Nerve in the Chelonians ? 

 The question has been already answered in the negative by 

 my experiments on the Terrapin. After making two tests 

 on the sea-turtle, the latter of which was in everyway satis- 

 factory, the variations in blood-pressure being indicated in a 

 rather sensitive way by a simple contrivance, it was impossi- 

 ble to find any fine nerve which produced marked lowering 



* Journal of Physiology, vol. v. Nos. 4, 5 and 6. 



