34 



Dr. J. A. Mc William. On the 



[Dec. 18, 



to the tail is not always the same. After the tail has been repeatedly 

 stimulated, with the effect of causing reflex muscular contraction 

 and cardiac inhibition, a phase (of exhaustion) often occurs, during 

 which stimulation fails to bring about either reflex movements or 

 cardiac arrest. 



The effects of the administration of strychnine (by hypodermic 

 injection) are in accordance with the phenomena already described. 

 After strychnine poisoning convulsive movements occur, as in the 

 frog, in response to stimuli of a very trivial character. But in the 

 eel, the advent of each convulsive attack is accompanied by a tem- 

 porary arrest of the heart's action. The vagus centre seems in this 

 instance also to be thrown into action in company with the ordinary 

 motor centres. 



Again, when experimenting with an eel, struggling movements of 

 the animal occasionally occur without any apparent cause. These 

 movements, if confined to the tail part, are accompanied by no per- 

 ceptible change in the heart's action, but when they involve the whole 

 length of the animal or the part next the head, cardiac arrest occurs 

 at the same time — just as cardiac arrest accompanies the struggling 

 movements resulting from stimulation of the skin of the head or 

 tail. When the motor centres of the cord and medulla (including the 

 respiratory centre) are paralysed in consequence of a prolonged 

 administration of ether or chloroform, the vagus centre also seems to 

 be liors de combat. Reflex inhibition of the heart does not then occur 

 as a result of the stimulation of any part, though direct stimulation 

 of the vagus nerve readily leads to prolonged inhibition. 



It will thus be seen that stimulation of the skin of the head and of 

 the tail of the eel is peculiarly effective in causing reflex inhibition of 

 the heart's action. The skin of the head and tail are shown to be 

 possessed of a specially high sensibility by results other than cardiac 

 arrest. For if a vigorous uninjured eel when lying quiescent on a 

 board be lightly touched on the head with the finger, reflex movements 

 of a more or less extensive and complex character are immediately 

 manifested. Similar results are obtained by holding between the 

 fingers or very gently compressing the tail ; the resulting movements 

 are sometimes confined to the caudal region, while they at other times 

 affect the whole length of the animal. But when the intermediate 

 tract of the eel's body is tested in the same way, it is found that no 

 visible effects of any kind follow the application of gentle pressure 

 to the skin. The skin of the animal's body seems to be quite irre- 

 sponsive to stimuli which produce striking effects when applied to 

 the head or tail. 



It would seem then that cardiac arrest is most readily excited by 

 stimulation of those cutaneous surfaces which are prone to yield reflex 

 movements as a result of similar stimulation. In other words, stimu- 



