316 THE OUTGO OF ENERGY 



A negative variation will be observed each 

 time the nerve is stimulated. 



2. The current of action is not dependent on 

 the electrical stimulation, but is an expression of 

 the changes in the nerve which constitute the 

 nerve impulse. It follows mechanical as readily 

 as electrical stimulation. 



Lead to the capillary electrometer from non- 

 polarizable electrodes placed on the longitudinal 

 surface and cross-section. Note the position of 

 the meniscus. Stimulate the nerve mechanically 

 by snipping the end with the scissors. 



There will be a negative variation as before. 



Positive Variation. The direction of the cur- 

 rent of action is not always opposite to that of 

 the demarcation current. Biedermann obtained 

 a current in the positive direction on stimulating 

 the nerve to the abductor muscle in the lobster. 

 In the tortoise, the cardiac auricle may be cut 

 away from the sinus, without injury to the cor- 

 onary nerve, which in this animal carries to the 

 auricle the cardiac fibres of the vagus. After 

 this operation, the auricle and ventricle remain 

 motionless for a time. In a heart thus prepared, 

 Gaskell made a thermal cross-section by im- 

 mersing the tip of the auricle in hot water, and 

 led the demarcation current to a galvanometer. 

 The stimulation of the vagus in the neck the 



