THE ELECTROMOTIVE PHENOMENA 295 



placed on the equator of the muscle (Fig. 47). 

 Bring the slider to the zero post. Bring the 

 meniscus into the field. Note its position on the 

 micrometer scale. Open the short-circuiting key. 

 When the meniscus comes to rest, move the slider 

 along the rheochord until the meniscus returns 

 to its original position. Eead the number of 

 millimetres between the positive post and the 

 slider. This number divided by 10,000 is the 

 fraction of the electromotive force of the Daniell 

 cell (1.1 volt) necessary to balance the current of 

 injury of the muscle (from 0.035 to 0.090 volt). 



DEMARCATION CURRENT OF NERVE 



Place non-polarizable electrodes on the cross- 

 section and longitudinal surface of a long piece 

 of sciatic nerve. Connect the electrodes through 

 a short-circuiting key with the electrometer. 

 Bring the meniscus into the field and open the 

 short-circuiting key. 



The meniscus will move in a direction indicating 

 a current in the nerve from cross-section to longi- 

 tudinal surface, as in muscle. 



Measure the electromotive force of this demar- 

 cation current. 



The demarcation current is much weaker in 

 nerve than in muscle, being in the former about 



