in ELECTRICAL EXCITATION OF MUSCLE 315 



seat of direct excitation (physiological anode and kathode), 

 than to the conditions of the propagation of the excitatory 

 process by conduction. In this sense the law may be expressed 

 as follows : 



As a rule, when current is applied to suitable objects, trans- 

 mission of excitation from the point directly stimulated occurs only 

 with sufficiently rapid alterations of current, whether starting from 

 zero, or from any given value. 



Comparative investigation of different contractile substances 

 shows directly that visible changes arise at the point of 

 excitation during the entire passage of current, and for some 

 time after, the significance of which is clear except in cases 

 where, e.g. in striated muscle, they are more or less over- 

 shadowed by the results of the transmitted excitation (" twitch "). 

 Without entering into. the question why there is, as a rule, only 

 one wave of contraction at closure, and opening, of the circuit, it 

 may be pointed out that the same effect occurs under certain 

 conditions with intermittent persistent excitation from homo- 

 dromous, rapidly interrupted currents, just as in other cases the 

 continuous closure of a battery current will produce a persistent 

 excitation of the entire muscle similar in appearance to that 

 caused by intermittent excitation. As regards the first, it was 

 shown by Bernstein and Engelmann that when the interval 

 between two consecutive closures of a rapidly interrupted battery 

 current, falls below a certain value, the effect of excitation upon 

 striated muscle is similar to that produced by closure of a con- 

 stant current ; i.e. a single wave of contraction (initial twitch) 

 starts from the kathode, at which, as in persistent closure, there 

 may be persistent local contraction. The magnitude of this 

 interval diminishes with increasing strength of current, and 

 increases with diminishing excitability. 



The same fact is still more easily demonstrated, according to 

 Engelmann, upon the sluggishly reacting ureter, since the pauses 

 between two consecutive closing stimuli may be much greater than 

 in striated muscle without alteration of the effect, inasmuch as a 

 wave of contraction only occurs at the beginning and end of the 

 intermittent excitation, starting in the one case from the kathode, 

 in the other from the anode (" initial and final twitch "). Under all 

 conditions a certain interval, varying greatly in different contractile 

 substances (where conductivity is in general more highly developed), 



