LAW OF PULSATIONS. 



135 



wliich represent the dependence of the excitement of 

 the nerve on the strength and dkection of the current, 

 are spoken of as the law of pulsations. This law is 

 represented in the following table, in which S signifies 

 closing, opening, Z pulsation, and R rest — i.e. no 

 pulsation — the duration of the currents being indicated 

 by the arrows. 



As soon as the nerve dies, the phenomena under 

 the law of pulsations change. If weak currents are 

 applied to a fresh nerve, which in either direction 

 produce pulsations only on the closing of the current, 

 and if then, the currents remaining entirely unaltered, 

 their influence on the nerve is tested from time to 

 time, it will be found that pulsations gradually begin 

 to occur on the opening of the current; these are at 

 first weak, but they continually become stronger till 

 they are fully equal in strength to the pulsations 

 resulting on the closing of the current. This condi- 

 tion is retained for some time, after which the closing 

 pulsations of the ascending current and the opening 

 pulsations of the descending current become weaker, 

 and finally entirely disappear, so that the descending 

 current produces only closing pulsations, and the 

 ascending current only opening pulsations ; and this 

 condition endures until the excitability at the points 

 examined is entirely expended, the pulsations be- 



