550 COMPARATIVE ELECTRO-PHYSIOLOGY 



either no response or an occasional flutter, in the positive 

 direction. 



We have thus seen, in the course of the present chapter, 

 that, in addition to the mechanical and electro-motive modes 

 of response, there is also a third mode available namely, 

 that by Resistivity Variation. We have also seen that the 

 results obtained under these three methods are identical. 

 It has been shown that the normal excitatory effect is in 



FIG. 332. Effect of Chloroform seen in Modification of Resistivity 

 Variation in Frog's Nerve 



The normal responses seen to the left by diminution or negative variation 

 of resistance were evoked by stimuli at intervals of one minute. 

 Those to the right exhibit the effect of chloroform. The normal 

 response is thus abolished, and we have either no response or only an 

 occasional flutter in the positive direction. 



all three cases negative, consisting of mechanical contraction, 

 galvanometric negativity, or diminution of resistance, as the 

 case may be. In recording the morographic curve by these 

 three methods, we find that up to the critical point of death, 

 at or near 60 C, we obtain expansion, galvanometric posi- 

 tivity, and increasing resistance. At that point, however, 

 there is a sudden reversal of the curve, indicating conversion 

 to negative, contraction, galvanometric negativity, and de- 

 crease of resistance. 



