, 



m 



: 



RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY 549 



case. It is thus seen that the response, by resistivity 

 variation, is an independent expression of the excitatory 

 variation. 



In taking records of the responses of animal and vege- 

 table nerves, by the methods of mechanical and electro- 

 motive variations, we saw that, while the normal response 

 was negative, this was liable to become reversed to positive, 

 under two different conditions namely, sub-tonicity and 

 the fatigue due to excessive stimulation. Similar reversals 

 are observed under similar conditions, when the method 

 of resistivity variation is employed. We saw, further, that 

 the abnormal positive response, due to sub-tonicity, could be 



adually converted into normal negative, through inter- 

 mediate diphasic, by tetanisation further tetanisation acting, 

 moreover, to exalt this feeble into enhanced negative 



sponse. Parallel results are observed in the case of 

 resistivity variation. The initial abnormal response, by 

 increase of resistance, is found, after short tetanisation, to 

 be converted into diphasic an increase of resistance or 

 positive response preceding the true excitatory or negative 

 effect of diminution of resistance. Further tetanisation 

 brought about the disappearance of this preliminary positive, 

 and the enhancement of the negative, response. 



I used the same method, finally, for the observation of 

 response and its modifications, by means of anaesthetics in 

 animal nerve. For this purpose I took a nerve of frog, and 

 subjected it to chloroform. It will be remembered that in 

 studying the effect of anaesthetics by the electro-motive 

 variation method, we found it, first, to reverse the normal 

 response to positive, and finally to induce an abolition, 

 which might prove to be either temporary or permanent. 

 The same thing is seen under the resistivity variation 

 method. In the first series of records, given in fig. 332, we 

 find normal responses by diminution of resistance, to a 

 series of stimuli applied at intervals of two minutes. 

 After the application of chloroform, the normal responses 

 are seen to have disappeared. Stimulus now evokes 



