CYCLIC MOLECULAR VARIATION 635 



method of electro-motive variation, before and after mechanical 

 tetanisation. The antecedent molecular transformation to 

 which this enhancement is due may also be gauged, in all 

 these cases, by the shifting of the base-line upwards. 



We have up to this time dealt with the first part only of 

 the characteristic curve, up to a point slightly above that of 

 transition. The responding substance, however, in con- 

 sequence of the after-effect of stimulation, now passes into 



FIG. 394. Photographic Record showing Responses corresponding with 

 different parts of characteristic curve in frog's nerve 



a, Abnormal subtonic ; b, Staircase ; c, Uniform ; d, Fatigue decline ; 

 e, Fatigue reversal. 



various different phases of molecular condition. These may 

 be short-lived, or more or less persistent. 



We shall next study all the responsive modifications due 

 to these induced molecular conditions, from the subtonic A 

 to the post-maximum E conditions, in order. Selecting as 

 our specimen for this purpose the nerve of frog, the different 

 phases through which this is capable of passing may, for 

 convenience, be divided into five classes (fig. 394). In the 

 first of these the abnormal A phase the nerve is sub-tonic. 

 It is here undergoing a relaxation, and its characteristic 



