CURRENT OF INJURY AND NEGATIVE VARIATION 159 



of slow recovery from the excessive stimulation of injury. 

 Response by negative variation is then found to undergo a 

 decline. It is in general vaguely accepted that, in order to 

 obtain a response by negative variation an 'antecedent current 

 of injury is necessary, by whose induced variation we may 

 be able to record responsive effects. In cases of the dis- 

 appearance of the current of injury, it is supposed that 

 response must necessarily vanish, since its antecedent con- 

 dition no longer exists. But I have already shown, and shall 



FIG. in. Record of Responses in Plant (Leaf-stalk of Cauliflower) 

 by Method of Negative Variation 



The first three records are for stimulus intensity I ; the next six are for in- 

 tensity twice as strong ; the successive responses exhibit fatigue. The 

 vertical line to the left represents 'I volt. The record is to be read 

 from right to left. 



have occasion again to show in the next chapter, that these 

 suppositions are altogether erroneous. For we may obtain the 

 usual response when the current of injury is zero, or even 

 positive. In fact, the only essential condition for the obtaining 

 of resultant response is that at one contact the excitability 

 should be in a state of relative depression. 



In that case in which response becomes enfeebled, with 

 the gradual decline and vanishing of the current of injury, 

 a simple explanation is often applicable. When the tissue is 

 injured, it does not necessarily die. In fact, I have often 



