H 



COMPARATIVE PHYSIOLOGY 



Sees. 



concentration cell. The action-current occurs in denervated 

 (Adrian) as well as normal muscle. It travels as a wave along 

 the length of the muscle like the mechanical response itself. 

 Any excited region becomes momentarily electronegative to an 

 unexcited part. The existence of this potential indicates a 

 redistribution of ions within the system in which the potential 

 difference is developed. One explanation, offered by Mines, 

 is that the sudden concentration of hydrogen ions at the 

 sensitive surfaces of the fibres sets up there a condition which 

 may be likened to that of a concentration battery. There are, 

 however, two very cogent objections of a general nature to this 



proposal. One is that the 

 electrical change in striped 

 muscle (see Fig. 3) is 

 practically complete before 

 the mechanical response 

 begins ; the negative varia- 

 tion occurs in the latent 

 period and begins con- 

 temporaneously with the 

 application of the stimulus. 

 It is thus probable that 

 tro-cardragramreToVherrtof Ho^ the electrical phenomenon 



is associated with events 

 antecedent to those with which Hill's hypothesis is concerned, 

 since Hill has shown that the production of acid continues 

 up to the point at which maximum tension is developed. This 

 conclusion is strengthened by the close similarity (Chapter VIII) 

 between the electrical accompaniments and physical conditions 

 which are associated with the initiation of the excited state in 

 nerve and muscle. Therefore the electrical response may be 

 considered more conveniently in relation to excitation in the 

 more restricted sense (Chapter VIII). It is of interest in 

 connection with Mines' hypothesis, however, to note that the 

 phase of negative variation is often succeeded by a second 

 phase which is developed at the beginning of the mechanical 

 response. Possibly the origin of the electrical phenomena is 

 itself complex. It is difficult to believe that a concentration 



