2] EFFECT OX STRUCTURE AND FUNCTIONS 133 



the nerve can be stimulated to its functions, but that muscle 

 from which the activity of the nerve has been excluded by the 

 use of curare (which inhibits the action of the nerve, but not 

 of the muscle), will contract upon the passage of a current. 



Upon the character of the current, however, depends that 

 of the response ; thus, although, as we have seen, a closed 

 constant current continues to stimulate Protista, it has been 

 said not to stimulate nerve or muscle. A contraction follows, 

 it has been maintained, only upon considerable variations in the 

 electrical condition, such as result from making or breaking 

 the current. It is probable, however, that there is not so great 

 a difference in responsiveness of muscle and Protista as would 

 seem to be implied, for BIEDERMAXX ('83) has shown that the 

 constant current produces a whole series of slight contractions 

 in muscle which cannot be regarded merely as a secondary 

 result of the making shock ; and FICK ('63) has observed 

 contraction due to the constant current in muscles of Lamel- 

 libranchia. So that even in muscles, there is an actual, though 

 weak, response to a steady, constant current. 



There are two phenomena following momentary shocks ap- 

 plied to muscles which deserve notice in passing. First, when 

 a single induction shock is passed directly through a muscle, 

 we notice that the contraction is not simultaneous with the 

 shock, but follows only after the lapse of a certain " latent 

 period." This latent period represents, it is believed, time 

 spent in transformations going on in the plasma preparatory to 

 contraction. Secondly, when we pass (especially in a muscle- 

 nerve preparation) a series of induction shocks, closely following 

 one another, as in the alternating current, a very violent con- 

 traction is produced, since the new shock comes to the muscle 

 before it has had time fully to relax, and causes a contraction of 

 the already contracted tissue. Thus stimulus is superimposed 

 upon stimulus, and a summated response (tetanus) takes place. 



We must now consider more carefully a subject to which 

 we have hitherto merely alluded, namely, the relation to the 

 electrodes of the point of the organism at which the response 

 first appears. Thus, when the amoeboid Pelomyxa is subjected 

 to the constant current, a contraction appears, at the time of 



