iv ELECTROMOTIVE ACTION IN MUSCLE . 439 



uniform conditions of experiment, to produce a negative variation in 

 only one direction. This is readily understood when we remember 

 that the negative effects preponderate greatly under normal 

 conditions, while the opposite positive variation appears properly 

 at a very limited range of the scale of excitation, while 

 later on it is masked completely. In order to abolish "it 

 altogether, it is only necessary, as a rule, with even weak 

 excitation, to keep the animals under experiment for several 

 hours in water at 20-25 C., or to leave the claws, cut off, 

 for some time (about an hour) in a moist chamber at normal 

 temperature. The adductor muscle then exhibits an electro- 

 motive reaction to excitation from the nerve, which is the exact 

 opposite to that of continuous activity. While the muscle thus 

 exhibits a negative variation in one direction only, both with 

 the minimal excitation from the nerve, and with maximal 

 currents (i.e. responds, like all other known voluntary, striated, 

 vertebrate muscles), the same muscle, under uniform conditions 

 of excitation and leading -off, will sometimes yield precisely 

 opposite electrical changes, expressed in a positive variation of 

 the demarcation current, which have so far found an analogue 

 only in vertebrate cardiac muscle. These two opposite variations of 

 the muscle current exhibit certain striking peculiarities, as regards 

 both strength and time-relations, when they appear as the sole 

 effect of excitation under the above conditions ; and these are 

 not without importance in the interpretation of the phenomena. 

 In the first place, it is found that in the one case, as in the other, 

 the magnitude of the deflections on the galvanometer is nearly 

 always greater, at uniform conditions, than it is in a perfectly 

 fresh normal muscle of a " cold crab." In such a preparation 

 the effect in one or the other direction is seldom more than 

 50 degrees of the scale, while in a fatigued adductor muscle the 

 positive deflections frequently amount to 100 divisions of 

 the scale, and the negative effects in preparations of " warm 

 crabs " are still more striking. 



In the normal adductor muscle again a prominent fact is the 

 rapid swing back of the negatively deflected magnet, on the 

 prolongation of strong excitation, although, as is easily proved, 

 the tetanisation of the muscle persists much longer. Not in- 

 frequently the scale flies beyond its zero, and remains deflected 

 in the sense of an opposite positive variation. A preparation that 



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