THE MYELIN BODIES. 375 



The amount of homocerebrin which may be obtained from pro- 

 tagon is about one-fourth that of cerebrin. It is isolated in associa- 

 tion with the latter, as described, and can be separated from the 

 cerebrin by fractional crystallization from the alcoholic solution, in 

 which it is more readily soluble than cerebrin, 



Encephalin. Encephalin is regarded as a transformation-product 

 of cerebrin, and, like this, yields galactose on boiling with dilute 

 mineral acids. Cetylid is also obtained on treating with concentrated 

 sulphuric acid. It is soluble in hot alcohol, but tends to separate 

 out on cooling as a jelly-like material. On slow evaporation it 

 crystallizes in platelets, which melt at 150 C., but are already 

 decomposed at 125 C. In hot water it swells to form a thick 

 paste, which remains on cooling. Like homocerebrin, the substance 

 is found in the alcoholic solution after the cerebrin has separated 

 out (see above), and can be isolated by fractional crystallization 

 from the mother-liquor, or from a solution of acetone, in which the 

 homocerebrin is likewise soluble. 



Lecithins. The lecithins, which may be isolated from nerve- 

 tissue, where they largely exist in combination with the cerebrosides, 

 in the form of protagon, but undoubtedly also occur as such in the 

 free state, are as yet but little known. On decomposition they 

 yield palmitic acid, stearic acid, oleic acid, glycerin-phosphoric acid, 

 and cholin. Of their significance nothing definite is known, but it 

 appears that they are in some manner intimately concerned in the 

 development of the cells, and it is for this reason probably that 

 much smaller amounts can be obtained from the embryonic brain 

 than from that of the adult. 



(For the general description of the lecithins, see p. 65). 



Isolation. To isolate the lecithins of the brain, the following 

 method, which has been suggested by Ziilzer, is conveniently em- 

 ployed. The brain, which must be perfectly fresh, is freed from 

 membranes, cut into thin pieces, and placed in a jar with ether. 

 The material should rest on a layer of cotton. After standing for 

 several days the ethereal extract is poured off, and separated from 

 the lower layer of blood. The extraction is continued with new por- 

 tions of ether so long as anything passes into solution. If desired, 

 the remaining material can then be extracted with 80 per cent, alco- 

 hol at 45 J C., which takes up the protagon, as has been described. 



The ethereal extracts are united and concentrated in the vacuum. 

 Any protagon that has passed into solution is thus thrown down 

 and filtered off. The clear solution is now treated with an excess 

 of acetone so long as a precipitate is formed. This is filtered off 

 and thoroughly washed with acetone. The acetone-ethereal solution 

 we term A, and the precipitate B. A, contains the entire quantity 

 of cholesterin. To recover this, the acetone-ether is distilled off, 

 the residue is boiled with alcohol, the alcoholic solution is filtered 

 while still hot, when, on cooling, the substance crystallizes out. Its 

 melting-point is 145 C. 



