CHAPTEE VIII 



CONDUCTIVITY AND EXCITABILITY OF NERVE 



I. PHENOMENA IN NERVE-FIBRES 



CONDUCTIVITY is the chief and indeed exclusive function of the 

 nerve-fibre, and the principal facts relating to it have next to be 

 considered. There is absolutely no fundamental difference in 

 the conducting of an excitatory process within any kind of 

 excitable conductive protoplasm, e.g. muscle and nerve. In both 

 cases normal continuity of structure seems to be an indispensable 

 condition of conductivity, the excitation, at least in nerve-fibres, 

 being directly transmitted from point to point. Eecent conclu- 

 sions as to the finer anatomy of the central system, on the 

 other hand, render it highly probable that there is here an 

 exception to the rule, inasmuch as the transmission of excitation, 

 more especially from ganglion -cells to nerve-fibres, and vice versa, 

 is effected not by continuity but by contact contiguity- only. 



It has already been pointed out in muscle that excitation 

 under certain normal conditions remains localised to the directly 

 excited fibre, and does not cross over into adjacent fibres. The 

 same is true of nerve, whether medullated or non-medullated. 

 Kuhne (9) succeeded in exciting single fibres of the frog's sciatic 

 by the unipolar method, upon which only the correlated muscle- 

 fibres contract. The isolation and independence of the single fibres 

 is confirmed by the effect of partially dividing a nerve-trunk ; 

 only a certain part of the tract supplied by the nerve will then 

 be paralysed. When a nerve-fibre bifurcates, the excitation of 

 the trunk is of course transmitted to all its branches. The 

 ramifications are most abundantly developed within the central 

 organs, but occur also in the peripheral terminations (muscles, 

 electrical organs, etc.), and even, though more rarely, along 



