MYOGENIC RHYTHMS 



101 



stimulation is already, by custom, the thing done to the excitable tissue 

 and excitation is its response. Excitation of the muscle fiber leads to an 

 active state in the muscle fiber as a whole ; this is the unknown process 

 labelled (4) in Fig. 1. Normally the active state produces, in turn, an 



Fig. 1. Hypothetical course of events in ex- 

 citation of long-fibered muscle through its motor 

 nerve. 



activation of the contractile mechanism (5), with development of tension 

 and/or contraction depending on the nature of the load. A corollary of 

 these definitions would be that tetanus means a maintained contraction or 

 a maintained tension and not a maintained active state which must be re- 

 ferred to as such. It is unfortunate that the terms used for processes (4) 

 and (5) should be so similar, and process (4) might perhaps better be 

 called priming of the contractile machinery by some form of coupling to 

 the surface events. The original terms as defined above will, however, be 

 used in this review. Clearly the distinction between active state and activa- 

 tion is only essential at present for insect fibrillar muscle, in which deacti- 

 vation by release aft'ects the contractile mechanism but not processes (3) 

 and (4). It may well prove, however, that such a distinction would be use- 

 ful also for other muscles. 



