192 ELECTRO-PHYSIOLOGY CHAP. 



single case, even with comparatively weak currents, since a 

 perceptible delay in the appearance of contraction (visible even 

 at a slow rate of the recording surface) is wanting, as a rule, 

 only in the weakest, minimal currents. The time-value of the 

 delay differs much in different preparations, and, as a rule, 

 diminishes in the same preparation with frequent repetition of 

 stimulus, even when the excitatory action of the current shows no 

 sign of diminution. 



Just as the inhibitory effect of stimulation is sometimes very 

 apparent in preparations of the adductor muscle (according to its 

 state), while in other cases it is merely indicated, or quite imper- 

 ceptible, notwithstanding an equal development of tonus a 

 variation that may essentially be due to altered conditions in 

 the muscle: so in the abductor, we find similar differences, 



FIG. 198. Abductor muscle of crayfish claw (atonic) ; excitation with (a) weak and (b) strong 

 battery currents ; in the last case there is a pronounced delay in the make contraction. 



although the inhibitory action here takes effect, as a rule, far 

 more certainly than in the antagonist muscles. 



The excitatory action of strong constant currents in the 

 adductor muscle (supra) so far preponderates over its inhibitory 

 effect that the latter only appears very exceptionally with strong 

 excitation, when a transitory relaxation may sooner or later 

 interrupt the closure tetanus. This is not equally true of the 

 abductor, where, even with strong currents, the inhibition (which, 

 as regards dependence on strength of stimulation, corresponds 

 with excitation in the antagonist muscles) is almost regularly 

 interrupted by the succeeding excitation in the course of a long 

 closure ; which excitation like the inhibition of the adductors 

 first effects entrance when the strength of the stimulus begins 

 to decline during the passage of the current. This last fact may 

 well cause the differences of effect on exciting with constant or 

 with tetanising alternating currents. 



