164 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



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 alcohoUc extract produces : this fall is 

 abolished, or even replaced by a rise of arterial pressure, if the animal has 

 been atropinised. 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. 



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.^ A chemical analysis of the nerves themselves was also made. A 

 series of cats was taken, both sciatic nerves divided, and the animals subse- 

 quently killed at intervals vax'ying from 1 to 106 days. The nerves remain 

 practically normal as long as they remain irritable, that is up to 8 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. The chemical explana- 

 tion of the Marchi reaction appears to be the replacement of phosphorised by 

 non-phosphorised fat. When the Marchi reaction disappears in the later 

 stages of degeneration, the non-phosphorised fat has been absorbed. This 

 absorption occmrs earlier in the peripheral nerves than in the central nervous 

 system. 



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

 degeneration of the pyramidal tract has been produced by a lesion in the 

 opposite hemisphere, and which gives the Marchi reaction, there is a similar 

 increase of water and diminution of phosphorus in the degenerated side. 



The table on next page shows these main results in the experiments on cats 

 just described. 



Cerebro-spinal tfuid. — This functions as the lymph of the central nervous 

 system, but differs considerably from all other forms of lymph. It is a very 

 watery fluid, containing, besides some inorganic salts similar to those of the 

 blood, a trace of proteid matter (globulin) and a small amoimt of a reducing 

 substance, the nature of which is uncertain. It is, however, not sugar, but is 

 possibly an aromatic substance allied to pyrocatechin. It contains the 

 merest trace of choline ; but this is not devoid of significance, for this fact 

 taken in conjunction with another — namely, that physiological saline solution 

 will extract from perfectly fresh nervous matter a small quantity of choline — 

 shows us that protagon is not a stable substance, but is constantly breaking 

 down and building itself up afresh ; in fact, undergoing the process called 

 metabolism. This is most marked in the most active region of the brain — 

 viz., the grey matter. 



and octahedral form, and 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. 



' The Marchi reaction is tbe 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 degenerated myelin is blackened 

 like the fat of normal adipose tissue. 



