period compared with that of the reflex evoked by the same strong stimulus 

 when applied as an initial one. In the first case, the synapse had been 

 already prepared, in the latter case, not. The latent period was, indeed, a little 

 shorter in the former case, but not sufficiently so to give any support to the view 

 mentioned. 



The delay must, therefore, be chiefly in the actual transmission, and not in 

 making the synapse conductive, nor in an amoeboid movement of protoplasmic 

 processes into contact with each other. 



Incidentally, the fact shows the importance of the cutting off by inhibition of 

 impulses which are not 

 wanted, since the channels 

 to the final common path 

 on the efferent side seem 

 to be always open ; no 

 preparation is needed. 



The latent time of a 

 reflex inhibition is no 

 longer than that of an 

 excitation. 



After-Discharge. The 

 discharge from a reflex 

 arc does not, as a rule, 

 cease when the stimulus 

 ceases, often lasting for 

 five seconds or more. The 

 duration is proportional to 

 the intensity of the 

 stimulus. With a weak 

 stimulus, the response may 

 not appear at all until 

 after the actual period of 

 stimulation has passed. 



The after-discharge can 

 be cut short sharply by 

 an inhibitory influence, as 

 shown in Fig. 107 (page 

 388). This rapid arrest 

 is an arrangement for 

 successive interchange of 

 reflexes. It prepares the 

 neurone for another stimu- 

 lation. 



Summation. A 1- 

 though, as we have seen, 

 there is a phenomenon of 

 this kind to be met with 

 in the case of nerve itself, 

 it is of a limited kind com- 

 pared with that shown by 

 reflexes. A scratch reflex cannot be elicited by a single induction shock, however 

 strong. On the other hand, very feeble shocks, if they follow one another at not 

 too short intervals, sooner or later evoke a response. In one case, no effect was 

 produced until after forty-four shocks at eighteen per second had been applied to 

 the skin. 



The flexion reflex, that is flexion of the knee produced by nocuous or 

 electrical stimulation of the skin of the foot, differs from nearly all other reflexes 

 by being elicitable by a single shock. 



Facilitation. This word is used by.Sherrington as a translation of " Bahnung." 

 One aspect of the phenomenon is the summation mentioned in the preceding 



FIG. 



150. PHOTOGRAPH OF C. S. SHERRINGTON. 

 (From a negative in the possession of 

 Mrs Sherrington. ) 



