CHAPTER IV. 



PROPERTIES OF NERVOUS FIBRES. 



THAT the cellular element is, in every nervous tissue, tl 

 important agent, that which plays the principal part, is beyoi 

 doubt j nevertheless it would give an incomplete idea of tl 

 nervous fibre to see in it only a conducting thread, which maj 

 be motory or sensitive indifferently, and solely by reason of its 

 terminal insertions. For example, it is not because the optical 

 nerve leads to the eye that it transmits or awakens only visual 

 sensations, since, after the section of this nerve, all excitation 

 conveyed to its central point arouses in the nervous centres 

 exclusively special sensations. We must therefore attribute to 

 the various orders of nervous filaments peculiar properties, in- 

 herent in their very structure, or rather in their molecular con- 

 stitution. This diversity is disclosed even by the manner 

 in which the nervous fibres die. Each order of fibres has its 

 peculiar kind of death. If, for example, we kill the nerves by 

 stopping circulation, we see the sensitive element die first, and 

 losing its properties from the periphery to the centre. Then 

 the motory element succumbs, but from the centre to the 

 periphery. The functional and nutritive centre of the motory 

 fibre is, then, the centre in which it ends. The fact is still more 

 clearly demonstrated by the section of a motory nerve. We see 

 then, as in the case of the stoppage of the circulation, this nerve 

 die from the centre to the periphery. To obtain movements by 



