7 6 



VETERINARY PHYSIOLOGY 



strictions of the neurilemma at the nodes of Ranvier (fig. 38). 

 It is composed of a sponge-work or felt-work of a horn-like 

 material neuro-keratin the meshes of which are filled with 

 a peculiar fatty material. 



The nerve fibres run together in bundles to constitute the 

 nerves of the body, and each bundle is surrounded by a dense 

 fibrous sheath, the perineurium. When a bundle divides, each 

 branch has a sheath of perineurium, and in many nerves this 

 sheath is continued, as the sheath of Henle, on to the single 

 fibres which are ultimately branched off from the nerve. 



2. Chemistry of Nerve 



The chemistry of neuron cells and their processes has been 

 deduced from a study of the chemistry of the grey matter of 

 the brain where they preponderate, while the chemistry of the 

 white sheath is indicated by the analyses of the white substance 

 of the brain, which consists chiefly of medullated fibres. 



FIG. 38. Pieces of two white Nerve Fibres. 



The grey matter contains over 80 per cent, of water. The 

 solids consist of rather less than 10 per cent, of proteins. 

 Two globulins, one coagulating at 47 C. and the other at 73' 

 to 75 C., and a nucleo-proteid coagulating at 56 to 60 C-, 

 have been isolated. Lecithin and cholesterin, each to about 

 3 per cent., are the other important constituents. 



The white matter contains only about 70 per cent, of 

 water. The proteins, similar to those in the grey matter, 

 constitute between 7 and 8 per cent. Lecithin occurs in 

 about the same amount as in the grey matter, but cholesterin 

 constitutes no less than l- r or 16 per cent. 



From the fatty material of the white sheaths various 

 complex substances have been isolated. The most abundant 

 of these has been called protagon. It yields stearic acid; 

 hence it is allied to the fats, and it contains nitrogen and 

 phosphorus. Its' constitution is not known. Along with 

 protagon, or as a result of its decomposition, lecithin occurs. 



