190 



ELECTRO-PHYSIOLOGY 



t.'HAP. 



While the tonus of the adductor muscle is, as a rule, inhibited 

 by minimal effective currents, without any perceptible excitation, 

 either previously or during prolonged closure, the first effect 

 of weak stimuli upon the abductor muscle is pre-eminently a 

 strengthening of the existing tonus ; and there is, in this par- 

 ticular, complete agreement between the effects of stimulation 

 with tetanising alternating currents and with the battery-current. 

 Even slight augmentation of the latter, however, in the one as 



FIG. 197. Abductor muscle of the crayfish claw (tonic) ; stimulation with constant currents of 

 increasing intensity ; augmented inhibition as primary effect of excitation. Time-marking 

 in seconds. 



in the other, brings out the striking dissimilarity, that each 

 single stimulus now produces double action. But while in the 

 adductor muscle excitation invariably precedes inhibition, the 

 contrary occurs in the abductor. At the moment of closing the 

 exciting circuit, excitation (contraction) in the one case, inhibition 

 (relaxation) in the other, makes a delayed entrance, and must in 

 each case be regarded as the primary effect of the current. 



As in the adductor muscle the consequent excitation seems, 

 at its first appearance, to be merely indicated, as an independent 

 constituent of the curve, so the same holds good of the effects 

 of inhibition, with indirect excitation of the abductor muscle. 



