202 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



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 is washed with absolute alcohol by decantation ; the precipitate is 

 then dissolved in 15-per-cent. alcohol, filtered, arid 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, 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. There is a danger of mistaking 

 such crystals for those obtained from the chlorides of potassium and am- 

 monium ; but the presence of such contaminations may be minimised by the 

 use of alcohol as water-free as possible. (2) The following test, however, 

 is entirely distinctive of choline and leads to no risk of confusion with other 

 substances. The final alcoholic solution prepared as above is evaporated to 

 dryness, and the residue taken up with water, to this is added a strong 

 solution of iodine (2 grammes of iodine and G grammes of potassium 

 iodide in 100 c.c. of water). In a few minutes dark-brown prisms of 

 choline periodide are formed. These look very like haemin crystals. If 

 the slide is allowed to stand so that the liquid gradually evaporates, the 

 crystals slowly disappear, and their place is taken by brown oily droplets^ 

 but if a fresh drop of the iodine solution is added the crystals slowly form 

 once more. (3) 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 pro- 

 duces : this fall is abolished, or even replaced by a rise of arterial pressure, if 

 the animal has been atropinised. Such tests have already been shown to be 

 of diagnostic value in the distinction between organic and so-called functional 

 diseases of the nervous system. 



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. 1 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 varying from 1 to 106 days. The nerves remain 

 practically normal as long as they remain irritable : that is, up to about three 

 days after the operation. They then show a progressive increase in the per- 

 centage 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. One chemical feature 

 of degeneration is the replacement of phosphorised by non-phosphorised fat. 

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



'' The Marchi reaction is the black staining that the medullary sheath of 

 degenerated nerve fibres shows when, after being hardened in Mailer's fluid, they are 

 treated with Marchi's reagent, a mixture of Miiller's fluid and osmic acid. Healthy 

 nerve fibres are but little affected by the reagent, but degenerated myelin is 

 blackened like the fat of normal adipose tissue. 



