iv ELECTROMOTIVE ACTION IN MUSCLE 437 



comparison with nornml preparations, even if deflections in the 

 direction of the negative variation occur on increasing the 

 stimulus. Eventually we obtained pure positive effects in one 

 direction by the application of a simple device, viz. fatiguing 

 the adductor muscle by unilateral exertion, until the reactions 

 from the motor nerves of the claw were reduced to a 

 minimum. 



In fresh, lively crabs it is easy to fatigue the adductor muscle 

 in a comparatively short time to such a degree that voluntary 

 or reflex contractions are only possible to a very limited extent. 

 It is only necessary to excite the muscle into vigorous con- 

 tractions, repeated as often as possible, by means of continuous 

 stimulation of the animal (insertion of a firm body and finger 

 between the joints of the claws). The extraordinary strength 

 and duration of the first contractions diminish with surprising 

 rapidity ; longer and longer pauses are required before the crab 

 can be stimulated to renewed, effective contraction of the claws, 

 and finally even painful excitation ceases to produce it. 



If a preparation thus fatigued is tested as above in regard to 

 its electromotive activity during excitation, it will be found 

 without exception that every trace of a negative variation is 

 wanting, while strong positive deflections accompany each effective 

 tetanisation of the nerve. The effect begins in different animals 

 within a tolerably wide range of current, increases to a certain 

 limit with approximation of the secondary and primary coil, to 

 decrease again, as a rule, with further increase of stimulus ; this 

 effect may perhaps be referred in part to an interference of the 

 two opposed effects of excitation, as is indicated inter alia by 

 the fact that at a lower degree of exhaustion of the adductor 

 muscle every possible transition occurs between diphasic action 

 with a predominance of positive deflection, decreasing in size 

 with increasing strength of current, and simple positive 

 variation. 



The independence of the galvanic effects of excitation 

 from any simultaneous change of form in the muscle, is quite 

 unmistakable in these experiments. In many cases mechanical 

 effects still appear in a fatigued preparation when it is strongly 

 excited from the nerve, and are expressed in a shortening of 

 the adductor muscle, which, however, is then accompanied, not 

 by a negative, but invariably by a positive variation of the 



