5 COMPARATIVE ELECTRO-PHYSIOLOGY 



to decline, owing to fatigue. In some other cases, moreover, 

 I have obtained a contraction of as much as 20 per cent. 



If we wish to obtain a series of successive responses, 

 however, it is desirable to avoid over-stimulation of the 

 tissue. In order, then, to obtain a response-record under 

 moderate stimulation, we have to employ a higher magni- 

 fication. This magnification, if made about 200 times, is 

 more than sufficient for all practical purposes, and the photo- 

 graphic records given in the course of the present chapter 

 are of this order. With long specimens of nerve, however, 

 a magnification of fifty times would be enough, and in the 



FIG. 313. Record of Contractile Response in Frog's Nerve under 

 Continuous Electric Tetanisation. 



Magnification, three times. 



course of the next chapters, I shall give certain records on this 

 scale, obtained directly on a smoked glass surface. The 

 apparatus used for the purpose was the Kunchangraph 

 (Sanskrit, kunchan, contraction), which I had already devised 

 aild employed in recording the contractile responses of plant- 

 tissues. This apparatus, as adapted for the purpose of 

 recording mechanical response in nerves, consists of, first, 

 a nerve-chamber, N ; secondly, a modified Optical Lever, O ; 

 and thirdly, a photographic recorder, D (fig. 314). 



Of these, the nerve-chamber consists of a small rectangular 

 ebonite box, the front of which is closed by a semi-cylindrical 



