NOTES AND ADDITIONS. 317 



we regard these processes as electric, in that the separate 

 fibres are not electrically isolated from each other. But 

 the explanation which we gave of the isolated excitement of 

 but one muscle-fibre by a variation of the electric current in 

 the appropriate nerve, also explains isolated transmission in 

 the nerve-fibres. For if the electrically active parts are 

 very small, comparatively powerful electric action can take 

 place in them, and yet the current may be quite unobserv- 

 able at a little distance. This is a consequence of the law 

 of the distribution of currents in irregular conductors, 

 explained in chapter x. 2. We must, therefore, assume 

 that the electrically active particles situated in the axis of 

 a nerve-fibre are small in comparison with the diameter of 

 the fibre, and that therefore their effect at the outer surface 

 of the fibre is already so weak that it cannot act and cause 

 irritation in an adjacent fibre. In Note 13 we have seen 

 that no action takes place by negative variation from one 

 fibre on an adjacent fibre. Our multipliers are much more 

 sensitive than nerve-fibres, so that the separate negative 

 variations during the tetanisation of the nerve can combine 

 their action on the multiplier ; but this is impossible in the 

 case of the excitement of nerve-fibres. 



