THE CHARACTERISTICS OF STIMULI 43 



some time, provided that the stimulation is not at once stopped. If 

 now during tetanic stimulation of the ninth root the eighth is at 

 the same time stimulated, with a strength of current equal to 

 that which previously brought about contraction of the muscle, 



Fig. 2. 



Lower thick line shows duration of stimulation of 9th root; upper thick line that of 



8th root 



instead of an increase and a strengthening of contraction there 

 is, on the contrary, an inhibition which continues throughout the 

 time during the stimulation of the eighth root. If the stimulation 

 of the eighth root is discontinued, the tetanic response of the 

 ninth root reappears. If, on the other hand, the faradic stimu- 

 lation of the ninth root is interrupted and the eighth root now 

 again stimulated, one obtains once more, as in the beginning, with 

 each stimulation a contraction of the muscle. This fact is illus- 

 trated by the accompanying tracings. (Figure 2.) In this inves- 

 tigation undertaken in the Gottingen laboratory it was further 

 shown that a faradic current of the same strength and the same 

 frequency had at one time an augmenting, at another an inhibitory 

 effect, and these effects could be produced alternately at will. 

 Should the faradic current at one time be called a stimulus, at 

 another not? It is here clearly shown to what absurd conse- 

 quences it leads if the conception of stimulation is limited solely 

 to the cases in which an external factor has an exciting effect ; 



