MECHANICAL RESPONSE OF NERVE 



517 



abolishes the response of nerve. But its preliminary effect 

 is often one of exaltation, as seen in fig. 3 1 8. 



I shall next describe the effect of chloroform, which dis- 

 plays many interesting features. We have seen that when a 

 tissue is excited by impinging stimulus, two opposite effects 

 are induced : one of these is the increase of energy, by the 

 absorption of stimulus, and the other is the expenditure 

 of energy by excitatory response. The former, as we have 

 seen, finds expression in galvanometric 

 positivity and expansion. The latter, 

 on the other hand, is exhibited as 

 galvanometric negativity and contrac- 

 tion. In the record of excitatory 

 response, the former of these elements 

 is generally masked by the predominant 

 negative or contractile effect. We have 

 also seen that this hidden positive may 

 be unmasked in either of two ways : 

 first, by retarding the expression of one 

 effect in relation to the other ; or, second, 

 by abolishing the excitatory negative 

 altogether. In the first of these cases, 

 the negative response is converted into 

 diphasic, say positive followed by 

 negative. In the latter, the response 

 becomes positive, by the suppression 

 of the negative. An example of this 

 unmasking of the positive element, by 



suppression of the negative, we have already seen to occur 

 under the action of chloroform (cf. fig. 49). This demon- 

 stration was made on a vegetable tissue, the test employed 

 being electrical. 



The experiment which I am now about to describe is 

 interesting from the fact that effects parallel to those there seen 

 in a vegetable tissue are in it shown to occur also in the highly 

 specialised animal nerve. The unmasked electro-positive 

 effect, moreover, is here seen to correspond with an expansive 



FIG. 318. Photographic 

 Record showing Pre- 

 liminary Exaltation in 

 Mechanical Response 

 of Frog's Nerve after 

 Application of Alcohol 



