IV 



ELECTROMOTIVE ACTION IN MUSCLE 



363 



of rest " as introduced by du Bois, has the distinct recommendation 

 that it shows the negative variation to be a deflection contrary 

 in direction to the original effect, its distribution in time, which 

 is accelerated at first with an aperiodic magnet, becoming gradually 

 slower. On prolonging the excitation there is a slow return tn 

 the position of rest, which is sometimes reached during the closure 

 of the circuit, in other cases only after it has been opened again ; 

 but the return is seldom perfect. There is usually a permanent 



FIG. 112. 



diminution of the muscle current (negative after-effect), the degree 

 of which depends on the strength of the previous excitation. 



The immediate inference as to the meaning of the backward 

 swing of the magnet during tetanus would be, that there was 

 a persistent diminution of the longitudinal current, continu- 

 ous throughout the period of excitation. In view, therefore, 

 of the known properties of the physiological rheoscope, which 

 reacts mainly at the rise or disappearance, or sudden variations 

 in density of a current, it might be expected that the leg serving 



