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 



/-/V 

 ' ' . ' X . . 



FIG. 116. 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) (o) 



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. (b) 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, #). The current of injury, c, is A->B, and 

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

 variation. 



