466 COMPARATIVE ELECTRO-PHYSIOLOGY 



described, then, the three types of response are exhibited by 

 the same tissue, in indubitable relation to the variation of 

 its effective conductivity. If, then, results exactly parallel 

 can be demonstrated to occur in the case of nerve also, it 

 follows that there is no necessity there to make any such 

 hypothetical assumption as that of the evolution of carbonic 

 acid, suggested by Dr. Waller, in explanation of the conver- 

 sion of abnormal response to normal. 



In order to show how a varying conduction will give rise 

 to these three types of responses, I shall now describe an 



fill ii 



FIG. 278. Abnormal Positive Response converted through Diphasic 

 to Normal Negative under the increasingly Effective Intensity of 

 Stimulus, brought about by Lessening the Distance between the 

 Responding and Stimulated Points 



experiment which I carried out with a frog's nerve in some- 

 what subtonic condition. Here, when the stimulator was 

 placed at some distance from the responding point, the 

 response was the abnormal positive (fig. 278). When the 

 effective intensity of transmitted stimulus was now slightly 

 increased by moving the point of application a little nearer, 

 the response became diphasic ; and finally, when the stimu- 

 lator was placed still nearer, the response became normal 

 negative. Thus with an identical specimen we may obtain 

 at will either negative, diphasic, or positive response, by 

 making changes only in the effective intensity of stimulus 

 employed. We have also seen, moreover, that if we kept 



