CYCLIC MOLECULAR VARIATION 637 



response records. From the inclination of the line thus pro- 

 duced it is possible to see whether the nerve at each different 

 phase was contracting, had assumed a stable length, or was 

 relaxing. In the B phase, as here shown, for instance, it will 

 be seen that the nerve, when undergoing an increasing con- 

 traction, shows a staircase enhancement of response ; at C 

 we observe this change to arrive at a climax, with con- 

 sequent stability of condition and uniformity of response. 



The characteristic curve, after this, undergoes a reversal : 

 that is to say, responsive contraction is now diminished, and 

 eventually gives place to relaxation ; and it is curious to find 

 that all the responsive phenomena observed during the 

 ascent are now repeated, but in the reverse order. That is 

 to say, during the ascent of the curve we obtained the se- 

 quence of abnormal positive, diphasic, and increasing normal 

 responses. And during the reversed process we obtain 

 diminishing normal, diphasic, and the culminating abnormal 

 positive response. The cycle of molecular phases, with their 

 attendant variations, is thus complete. 



An inspection of D shows the change in the condition of 

 the nerve from the contracted to the relaxing state. The 

 onset of fatigue is also seen in the diminishing amplitude of 

 the responses. This process is seen accentuated, to the 

 actual reversal of response, in the last phase E. I shall later 

 give a special record exhibiting the diphasic responses inter- 

 mediate between D and E. 



The response of nerve has hitherto been supposed, as 

 already mentioned, to be specifically different from that of 

 ordinary tissues. One characteristic particularly insisted 

 upon was its indefatigability, or incapacity for fatigue, the 

 nerve in this respect differing essentially from the muscle. 

 On taking a general review, however, of nerve and muscle- 

 response, we find that there is no essential difference between 

 the two. During the first phase of contraction, both alike 

 show staircase increase. This is followed, in both, by a 

 series of uniform responses. And in the stage of fatigue, 

 in both, the process of contracture gives place to one of 



