THE ELECTROMOTIVE PHENOMENA 297 



of respiration, presumably by the stimulation of 

 the nerve through the closure of its own demar- 

 cation current by the lymph or blood, though 

 the possible influence of demarcation currents 

 from the wounded tissues cannot be forgotten. 

 Definite results, such as inhibition of the heart, 

 have not been observed to follow the closure of 

 the current of the peripheral segment. To avoid 

 any chance stimulation from the closure of the de 

 marcation current, nerves are sometimes severed 

 physiologically by freezing, a process which 

 not only does not stimulate, but which does not 

 destroy permanently the conductivity ; the latter 

 returns upon the restoration of the nerve to 

 normal temperature. 



The olfactory nerve of the pike shows a strong 

 demarcation current, as does the optic nerve. 



HYPOTHESES REGARDING THE CAUSATION OF 

 THE DEMARCATION CURRENT 



Make artificial cross-sections in a sartorius 

 muscle, and test the difference of potential be- 

 tween the longitudinal surface and a cross-section 

 with the electrometer. Divide the muscle, longi- 

 tudinally, and make fresh cross-sections ; test the 

 difference of potential again. 



However small the muscle prism may be 



