438 ELECTRO-PHYSIOLOGY CHAP. 



muscle current. In other cases again, all change of form is 

 wanting in the muscle, even with the strongest excitation, while, 

 on the other hand, the positive variation comes out in apparently 

 undiminished proportions. We observed the same phenomenon 

 in the adductor muscle of a crab, in which all the muscles had 

 undergone pathological change, and looked gray, as if from 

 boiling. These experiments show definitely that a positive 

 variation of the muscle current may appear in consequence of 

 nerve excitation, not merely when the muscle in tonic contraction 

 relaxes, but also when it is free from tonus and exhibits no 

 change of form on excitation, or even shortens slightly. .With 

 regard to the time-relations of the positive variation, it must be 

 observed that the beginning of the deflection coincides, as a rule, 

 with the beginning of excitation, so that in prolonged tetanus of 

 the nerve the scale remains some time at maximal deflection ; 

 when the circuit is broken it returns to its position of rest 

 with declining rapidity, but fails (in the initial excitations) to 

 reach it completely, so that the muscle current at first increases 

 steadily in consequence of nerve excitation. 



If a preparation which is in such a state that every effective 

 excitation produces only a positive variation of the muscle current, 

 is kept for a long time at a low temperature, and the effect of 

 exciting the nerve is periodically tested, it is found that 

 the deflections under similar conditions, with uniform strength 

 of coil and duration of closure, are gradually lessened, and even 

 change their sign under certain conditions, since with strong 

 excitation a weak negative variation appears again, either as the 

 prelude to a stronger positive variation, or independently. Thus, 

 after a long rest, a fatigued muscle preparation may return more 

 or less to the normal, characterised by diphasic galvanic effects 

 of excitation. The changes referred to are independent of the 

 simultaneous diminution of the muscle current, which may easily 

 be excluded by further supplementary injury to the parts of 

 the muscle still uninjured. If, as has just been stated, it is 

 possible to throw the adductor muscle of the crab's claw by 

 prolonged and exhaustive activity from the central organ on the 

 one hand, and on the other (though less certainly) by poisoning 

 with curare, into a state in which tetanisation of the corresponding 

 nerve produces only a positive variation of the muscle current, 

 it is still easier to exclude this last effect entirely, and, under 



