132 niYSIoUHJY OF MI-n.KS AND NKKYKS. 



present in tin- ner\e for -Mine time, a scrips of pulsa- 

 tions or :in apparent tetanus is occasionally observed. 

 Thi.- phenomenon lias long been known as an opening 

 t claim.-, "i- as // /'///"* ///// /fx. Tin- comic. 1 ion existing 

 between these changes in the excitability, and the fact 

 that the nerve may be' excited by electric current-, ha- 

 led to the adoption of a \ ie\v of t he elect ric excitement 

 in nerves which we shall not be able to develop until we 

 have more closely studied electric excitement itself. 



3. If a continuous current is passed through a nerve, 

 and is alternately closed and opened, the excitement 

 appears to occur irregularly, sometimes at the closing, 

 -"met imes at the opening of the current, and occasion- 

 ally even at both. Closer observation has, however, 

 shown that very definite laws control this. pro\ ided that 

 attention is paid to the strength of the current and its 

 direction within the nerve. Let us tir.-t examine these 

 phenomena as they occur in fresh nerve, and, as we found 

 that the conditions in the nerve change very rapidly 

 in the neighbourhood of the cut end, let us commence 

 onr observations at a low point in a fresh nerve, of 

 which as great a length as possible has been extracted. 

 For this purpose it is especially neces-ary to possess a 

 convenient mean- of graduating at will the strength of 

 the applied currents. Various methods have been used 

 for this purpose. The best is that which is based on 

 the distribution of the currents in branching conduc- 

 tors. The electric current, on being made to traverse 

 a conductor which sepaiates at any point into two 

 branches, divides, the stiviiv.th of the currents distri- 

 buted into these two branche- no) being ahvav- eipial, 



but being in each branch in Inverse ratio to the resis- 

 tance offered in that branch. Supposing thai the nerve 



