RESPONSE BY POSITIVE VARIATION 



175 



reversed injury-current is represented as down, the subse- 

 quent excitatory responses are also down, and constitute a 

 positive variation of the current of injury. 



It will thus be seen that an identical excitatory reaction 

 of the living tissue appears to give rise to directly opposite 



FIG. Ti6. Photographic Records of Responses of Vegetable Nerve, 

 one end of which has been injured 



In the first injury was slight ; current of injury represented up, response 

 by negative variation. In the second, injury greater ; injured point 

 neutral, response down. In the third, injured point killed ; injury 

 current reversed down, response by positive variation. 



effects namely, a negative or a positive variation of the 

 injury-current. 



I give below a short summary of the diversities of 

 response which may occur when either the natural, or the 

 injury-current, is taken as the current of reference. 



(a) 



Cb) 



FIG. 117. Typical Cases of Variation of Current of Rest and Action- 

 Current. Specimen originally isotropic 



(a) A, end slightly injured and negative ; c, current of injury ; R, action- 

 current, a negative variation of c. (<$) A, end killed and positive ; 

 c, current of injury ; R, action-current, a positive variation of c. 



First we take the case where the point A is slightly 

 injured (fig. 117,0). The current of injury, c, is A->B, and 

 the responsive current, R, is B -> A, constituting a negative 

 variation. 



