338 MANUAL OF HISTOLOGY. 



190. 



Of the chemistry of nervous tissue, but little is known on account of its 

 anatomical peculiarities; for, in the first place, the most massive nervous 

 apparatus, namely, the cerebro-spinal, which is on account of its bulk 

 most frequently the object of chemical research, has a very complex struc- 

 ture, and in it together with a ground-work of connective-tissue, we have 

 to deal with nerve tubes and ganglion cells which cannot be separated. 

 On the other hand, but little has been done to elucidate the nature of the 

 albuminous substances of the neural apparatus, and much obscurity still 

 hangs over the so-called cerebral matters ( 20). 



The living nerve displays, while at rest, a neutral reaction which be- 

 comes acid at death. The same change is produced, also, according to 

 Funke, by over excitement of the fibre. This is but a repetition of what 

 takes place in muscle under similar circumstances ( 170). 



From the anatomical study of the various parts of ganglion cells, we 

 know that the latter are made up of albuminous compounds, in which 

 fatty molecules and granules of pigment may be present ( 178). 



We have seen likewise (p. 307) that the sheaths of nerve fibres consist 

 of a substance resembling elastin, but more soluble than the latter in 

 alkalies, whilst the axis cylinder is composed essentially of several matters 

 belonging to the protein group, and the medullary sheath principally of 

 cerebrin. 



All that is known of the chemical composition of nervous tissue has 

 been learnt almost exclusively from examination of the substance of the 

 brain. 



The specific gravity of nervous trunks is 1-031, according to the obser- 

 vations of Krause and Fischer ; that of the white matter of the cerebel- 

 lum 1-032, of the cerebrum 1O36, and of the spinal cord 1-023, whilst 

 for the grey substance of both cerebrum and cerebellum we find 1-031, 

 ai\d for that of the cord 1-038. From several experiments which have 

 been made, it would appear that cerebral substance possesses in a high 

 degree the power of absorbing water. 



The amount of the latter in nervous tissue is subject to much variation. 

 In some cases it is but moderate, and in others it may become very con- 

 siderable. The proportion of water, for instance, in the peripheral nerves 

 is estimated by Schlossberger at 70-78, or even 80 per cent., that in the 

 white substance of the brain at between 69-64-70-68, and in the grey 

 matter 84-84-86-64, showing that the latter is richer in aqueous consti- 

 tuents. In the infant the brain is still poorer in solids. In the spinal 

 cord the percentage of water is lower, being, according to Bibra, 66 per 

 cent. Of course this water is distributed over both the tissue and the 

 nutritive fluids saturating the latter. 



As already mentioned, nervous matter consists of several albuminous 

 bodies of cerebral substances (lecithin and cerebrin), together with mineral 

 constituents. Finally, it contains certain decomposition products. 



Touching the albuminous matters, we are here more than elsewhere in 

 the dark as regards their nature. Our slight unacquaintance with the 

 chemical constitution of nerve cells only permits of our accepting the 

 presence of one or more members of the group in general, but gives no 

 indication as to what substance or substances occur specially. 



Tho reactions of the axis cylinder are those of an albuminoid substance 

 in a coagulated condition. But how far other albuminous matters may 



