658 



COMPARATIVE ELECTRO-PHYSIOLOGY 



part of the record which lies beyond the point of transition, 

 we can see that the excitatory change at first increases very 

 rapidly, and afterwards more slowly, under successive equal 

 increments of stimulus-intensity. 



In order to test the universality of these characteristics of 

 nerve-responses, I obtained records with many different 

 specimens. The record just shown was taken, as already 

 said, with a sciatic nerve of gecko, which was in somewhat 

 sluggish condition. The next (fig. 401) was obtained from 

 the sciatic nerve of a vigorous bull-frog. On subjecting this 

 nerve to increasing stimuli, r, 2, 3, 4, ... it was found that 



the positive response reached 

 a maximum, after which it 

 declined, and the response be- 

 came diphasic. With gradu- 

 ally increasing stimulus, the 

 positive element in the re- 

 sponse now became smaller 

 and smaller, while the negative 

 grew larger. Above this the 

 negative responses underwent 

 a very rapid increase. 



Up to this point, I have 

 been describing the peculiari- 

 ties of response, as seen in 

 motor nerves. In order to show, however, that the same 

 characteristics hold good of the responses of sensory nerves, 

 I next took a specimen of the optic nerve of Ophiocephalus. 

 As I here wished to demonstrate the possibility of the response 

 after continuous increase, reaching a limit, I employed the very 

 moderate magnification of only thirty times, in the recording 

 Kunchangraph. With larger magnifications, the record 

 exceeds the recording-plate, and such a demonstration is 

 impossible. The object being thus to record the peculiarities 

 of response in the negative region only, that stimulus which 

 was taken as the unit was sufficiently strong to induce a 

 contractile response which, under the given magnification, 



FIG. 401, Response of Nerve of 

 Bull-frog to Stimuli i, 2, 3, 

 . . . 12, increasing in Arithmetical 

 Progression 



