188 ELECTRO-PHYSIOLOGY CHAP. 



not necessarily the maximum of contraction ; while, on the other 

 hand, the duration of closure tetanus increases also, thus account- 

 ing for the fact that the obvious inhibition (relaxation) at each 

 single stimulus begins so much later after the beginning of 

 excitation (closure) in proportion as the current is strengthened. 



If the successive alterations which occur in contraction are 

 considered synthetically, there appears to be a gradual transition 

 from increasing and more or less extended twitches to definite 

 and prolonged closure tetanus ; which recalls the similar reaction 

 of the relaxed atonic muscle under the same conditions. Make 

 twitches of characteristic brevity occur not infrequently at a 

 certain strength of current, their curves being distinguished by 

 a very sharp apex : these presumably represent the effects of 

 inhibition following rapidly upon closure, since the curve of make 

 twitches under normal conditions is extended. 



The beginning and end of a series of experiments on atonic 

 adductor muscle are usually characterised by single (and oppo- 

 site) signs of excitation, with many intermediate transitions of 

 action, which, according to the strength of current, exhibit a 

 regular antagonism between excitation and inhibition, contraction 

 and relaxation. 



As shown by all previous experiments, inhibitory action 

 appears singly (in indirect excitation of the adductor muscle by 

 constant currents) at comparatively low intensity of current only ; 

 while very strong currents have an exclusively exciting action- 

 at all events, this is the rule immediately after closure. 



It should be further observed with regard to the abductor 

 muscle of the crayfish claw, that when once the exciting current 

 is sufficient to produce a perceptible reinforcement of the existing 

 tonus at closure, this effect under all circumstances precedes the 

 subsequent diminution of tonus due to inhibition. 



In the curve this only appears at first as a slight rise, 

 previous to the deep depression described by the lever in 

 consequence of the sinking (from inhibition of tonus) of the 

 free, and downward directed, arm of the claw. With each 

 stronger stimulus, the consequences of excitation are seen more 

 plainly, while those of inhibition are at first equal, and then, 

 owing to the increasing closure tetanus, make a more and more 

 delayed entrance. 



The curve at first rises steeply from the initial abscissa (which 



