MUSCLE AND NEEVOUS TISSUE 201 



keratin (especially abundant in white matter) is included in the above table 

 with the proteins. The granules in nerve cells (Nissl's bodies), which stain 

 readily with methylene blue, are nucleo-protein in nature. The next most 

 abundant substances are of a fatty nature ; the most prominent of these is 

 the phosphorised fat called lecithin (see p. 25). A complex substance 

 called protagon, which crystallises out on cooling a hot alcoholic extract 

 of brain or other nervous structures is of uncertain composition. Cerebrin 

 is a term which probably includes several substances, which are nitro- 

 genous glucosides ; they yield on hydrolysis the sugar called galactose 

 (see p. 18). They are sometimes called cerebrosides. There are other 

 phosphorised fats as well, of which kephalin is the best known. The crystal- 

 line monatornic alcohol cholesterin (see p. 93) is also a fairly abundant con- 

 stituent of nervous structures, especially of the white substance of Schwann. 

 Finally there are smaller quantities of other extractives, and a small pro- 

 portion of mineral salts (about 1 per cent, of the solids). 



Fresh nervous tissues are alkaline, but like most other living structures, 

 they turn acid after death. The change is particularly rapid in grey matter. 

 The acidity is due to lactic acid. 



Very little is known of the chemical changes nervous tissues under- 

 go during activity. We know that oxygen is very essential, especially 

 for the activity of grey matter ; cerebral anaemia is rapidly followed by loss 

 of consciousness and death. Waller has suggested that small quantities of 

 carbonic acid are produced during activity, because the increase in the action 

 current (detected by the galvanometer) which occurs after a nerve has been 

 repeatedly excited is very like the increase also noted on the application of small 

 quantities of this gas. Waller's suggestion has recently been confirmed by 

 direct experiments in which the amount of carbon dioxide formed has been 

 estimated. Large quantities of carbonic acid act like an anaesthetic, abolishing 

 nervous activity. Of all parts of the nervous system, the cells in the grey 

 matter are those which most readily manifest fatigue ; the next most sensitive 

 region is the termination of nerves in such endings as the end-plates. Fatigue 

 in a medullated nerve-trunk has never yet been experimentally demonstrated ; 

 Waller's view that this is due to inter-nutritional changes between the axis 

 cylinder and the investing medullary sheath can hardly be considered 

 proved, for it is just as difficult to demonstrate fatigue in non-medullated 

 nerves. 



Chemistry of Nerve-degeneration. Mott and I have shown that, in the 

 disease General Paralysis of the Insane, the marked degeneration that occurs 

 in the brain is accompanied by the passing of the products of degeneration 

 into the cerebro-spinal fluid. Of these, nucleo-protein and choline a decom- 

 position product of the lecithin (see p. 26) are those which can be most readily 

 detected. Choline can also be found in the blood. But this is not peculiar 

 to the disease just mentioned, for in various other degenerative nervous 

 diseases (combined sclerosis, disseminated sclerosis, meningitis, alcoholic 

 neuritis, beri-beri, &c.) choline can also be detected in these situations. The 

 tests employed to detect choline are mainly three : (1) The fluid is diluted 

 with about five times its volume of alcohol and the precipitated proteins are 

 filtered off. The filtrate is evaporated to dryness at 40 0. and the residue 



