QUANTITATIVE STIMULATION OF NERVE 



457 



shocks, we have seen that the resultant response is due to 

 the differential excitabilities of the two nerve- contacts A and 

 B. If, for instance, we wish to obtain the responsive reaction 

 of one point only, say A, uncomplicated by that of B, it is 

 only necessary to abolish the excitability of the latter. This 

 can be done to a greater or less extent by injury, as, say, by 

 making a transverse section, or by scalding. Response will 

 then take place by the induction of relative galvanometric 

 negativity at A. In fig. 274 is seen 

 a series of records obtained in this 

 manner. The responses here apparently 

 indicate growing fatigue of the nerve. 

 They also exhibit the positive after- 

 effect. 



With reference to the method of 

 obtaining response by injuring one con- 

 tact, commonly employed, it may be 

 said that the assumption that the ex- 

 citability of the injured point is totally 

 abolished is not justified ; for I have 

 found that though recent injury causes 



a great depression of excitability, yet FlG> 274 . Re&ponse ~ of 

 after a lapse of time the injured point 

 tends to recover its excitability to a 

 greater or less extent. In such a case 

 we may expect two different effects to 



Frog's Nerve under 

 Simultaneous Excita- 

 tion of both Contacts, 

 by Equi - alternating 

 Electrical Shocks, one 

 Contact being Injured 



be exhibited in the responses. The re- Note the positive after- 

 sultant response being due, as we have 

 seen, to the differential excitability of A and B, the gradual 

 restoration of the excitability of B will progressively diminish 

 the amplitude of the resultant response, thus giving it the 

 appearance of fatigue. Under these conditions, and after 

 a sufficiently long interval, response may almost disappear. 

 This appears to me to be the true explanation of the gradual 

 fall in the amplitude of response, when the specimen is a 

 nerve, having one contact at the transverse section. It also 

 explains why, in such a nerve, a fresh section, causing 



