436 PRACTICAL PHYSIOLOGY 



soap, the cholin is liberated and goes into solution, and the glycerin 

 and phosphoric acid remain combined with one another as glycerin- 

 phosphoric acid. 



In order to obtain these decomposition products, it is not necessary to 

 prepare pure lecithin as described above. All that is necessary is to 

 extract the yolks of several eggs with warm ether in a Soxhlet's 

 apparatus. The ether is then evaporated off and the residue, which 

 will contain lecithin, boiled in an evaporating dish with baryta water, 

 prepared of such a strength that, for each yolk used, 5 grammes of solid 

 barium hydrate and 50 c.c. of water are employed. The boiling should 

 proceed for about one and a half hours, water being meanwhile added 

 to replace that which is lost by evaporation. The solution is then 

 filtered to remove the insoluble soaps which have formed, and the 

 filtrate is freed from barium by passing a stream of carbon dioxide 

 gas through it. The barium-free filtrate is then divided into two parts 

 A and B. 



A is slowly evaporated to dryness, and the residue melted in 

 the silver basin with nitre and caustic potash, the melt dissolved 

 in water, and the phosphorus is precipitated. The presence of 

 phosphorus shows that the extract contained glycerin-phosphoric 

 acid, as any free phosphates, which may have been contained in the 

 ethereal extract of yolk, would have combined with the baryta to form 

 an insoluble salt. 



B is also evaporated to dryness, and the residue extracted with 

 absolute alcohol and filtered. The alcoholic extract is treated with 

 an alcoholic solution of platinic chloride (1 in 10). After standing an 

 hour or so, the precipitate of the double salt of cholin and platinic 

 chloride, which separates out, is filtered off, washed with alcohol, and 

 then dissolved in water. The watery solution is placed in a 

 desiccator over sulphuric acid, when the cholin salt crystallises out as 

 six-sided orange-coloured plates. 



Lecithin forms the chief constituent of the medullary sheaths of 

 nerves, and consequently can be obtained in great abundance by 

 extracting the white matter of the brain with warm alcohol. Such an 

 extract on cooling deposits crystals of a body called Protagon, which 'On 

 boiling with baryta water yields, besides the decomposition products of 

 lecithin, a body called Cerebrin, which contains nitrogen, and yields on 

 hydrolysis with an acid a carbohydrate which has been identified as 

 galactose. 



It is said that when nerve degeneration is taking place, as in inflam- 

 matory affections of the nervous system, cholin is detectable in the 

 cerebro-spinal fluid and in the blood (Halliburton and Mott). 



