CH. XV.] CHEMISTRY OF NERVE DEGENERATION 177 



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. 



Little or nothing is known of the chemical changes nervous tissues undergo 

 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. We have already seen that similar respiratory exchanges, though 

 less in amount, are stated to occur in peripheral nerves (see p. 171). 



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-proteid and choline a decomposition pro- 

 duct of the lecithin 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, etc.) choline can also be detected 

 in these situations. The tests employed to detect choline are mainly two : (1) a 

 chemical test, namely, the obtaining of the characteristic yellow octahedral crystals 

 of the platinum double salt from the alcoholic extract of the cerebro-spinal fluid or 

 blood ; * (2) a physiological test, namely, the lowering of arterial blood-pressure 

 (partly cardiac in origin, and partly due to dilatation of peripheral vessels) which a 

 saline solution of the residue of the alcoholic extract produces : this fall is abolished, 

 or even replaced by a rise of arterial pressure, if the animal has been poisoned with 

 atropine. It is possible that such tests may be of diagnostic value in the distinction 

 between organic and so-called functional diseases of the nervous system. The 

 chemical test can frequently be obtained with 10 c.c. of blood, or even less. 



A similar condition can be produced artificially in animals by a division of 

 large nerve trunks ; and is most marked in those animals in which the degenerative 

 process is at its height as tested histologically by the Marchi reaction, f A series 

 of cats was taken, both sciatic nerves divided, and the animals subsequently killed 

 at intervals varying from 1 to 106 days. The nerves remain practically normal as 

 long as they remain irritable, that is up to 3 days after the operation. They then 

 show a progressive increase in the percentage of water, and a progressive decrease 

 in the percentage of phosphorus until degeneration is complete. When regeneration 

 occurs, the nerves return approximately to their previous chemical condition. 

 When the Marchi reaction disappears in the later stages of degeneration, the non- 

 phosphorised fat has been absorbed. This absorption occurs earlier in the peripheral 

 nerves than in the central nervous system. 



Further, it has been found that in spinal cords in which a unilateral degenera- 

 tion of the pyramidal tract has been produced by a lesion in the opposite hemi- 

 sphere, there is a similar increase of water and diminution of phosphorus on the 

 degenerated side. 



The following table shows these main results in the experiments on cats just 

 described. 



* This test is performed as follows : the fluid is diluted with about five times its volume of 

 alcohol and the precipitated proteids are filtered off. The filtrate is evaporated to dryness at 40 C. 

 and the residue dissolved in absolute alcohol and filtered ; the filtrate from this is again evaporated to 

 dryness, and again dissolved in absolute alcohol, and this should be again repeated. To the final 

 alcoholic solution an alcoholic solution of platinum chloride is added, and the precipitate so formed is 

 allowed to settle and washed with absolute alcohol by decantation ; the precipitate is then dissolved 

 in 15-per-cent. alcohol, filtered, and the filtrate is allowed to slowly evaporate in a watch-glass at 40 C. 

 The crystals can then be seen with the microscope. They are recognised not only by their yellow 

 colour and octahedral form, but by their solubility in water and 15-per-cent. alcohol, but also by the 

 fact that on incineration they yield 31 per cent, of platinum and give off the odour of trimethylamine. 



t The Marchi reaction is the black staining that the medullary sheath of degenerated nerve-fibres 

 shows when, after being hardened in Miiller's fluid, they are treated with Marchi's reagent, a mixture 

 of Miiller's fluid and osmic acid. Healthy nerve-fibres are not affected by the reagent, but normal 

 adipose tissue is blackened like degenerated myelin. The osmic acid reaction is due to fats like olein. 

 which belong to the acrylic series. 



M 



