THE MYELIN BODIES. 391 



acids, glycerin-phosphoric acid, cholin, and in addition cerebrosides, 

 of which three are now recognized. These are known as cerebrin, 

 kerasin, or homocerebrin, and encephalin. Others also may possibly 

 exist, and it is likely that the pyosin and pyogenin, which Kossel 

 and Freitag obtained from pus, belong to this order. 



On boiling with dilute mineral acids protagon also yields a re- 

 ducing substance, which is commonly regarded as galactose, and is 

 referable to the decomposition of the cerebrosides just mentioned. 



Protagon is easily soluble in warm alcohol and ether, while in 

 cold alcohol and cold ether it dissolves with difficulty. On cooling 

 the substance crystallizes out in fine needles or in waxy masses, 

 which can readily be broken up into a fine powder. On heating its 

 alcoholic solutions to a temperature of 48 C. or on boiling its 

 ethereal solutions the substance is readily decomposed into its com- 

 ponents, as indicated above. In the dry state it can be heated to 

 a higher temperature, but it is then also decomposed before 100 C. 

 is reached. The resulting products melt between 200 and 203 C., 

 and begin to volatilize at 220. When moistened with water, the 

 substance swells and is partly decomposed, with the formation of 

 so-called "myelin" droplets. If much water is added, an opaque 

 fluid is obtained. 



Isolation. To isolate protagon from brain-tissue this should be as 

 fresh as possible, as otherwise partial decomposition occurs spon- 

 taneously. The material is freed from its membranes and adhering 

 blood, and is then stirred to a pulp, and extracted with 85 per cent, 

 alcohol, at a temperature of 45 C., using fresh portions of alcohol 

 from time to time until a specimen no longer deposits a sediment 

 when cooled to C. The extracts are filtered at 45 C., and sub- 

 sequently kept at C. The resulting precipitates are extracted 

 with cold ether to remove cholesterins and lecithins, when the 

 remaining material is pressed between filter paper and dried over 

 sulphuric acid. It is finally pulverized, again extracted with alcohol 

 at 45 C., when the solution is filtered and cooled to C. To 

 purify the substance it is recrystallized from warm alcohol or ether. 



Cerebrin. Cerebrin, as I have stated, is a normal decomposition- 

 product of protagon, but probably does not occur in the living 

 nerve-tissue as such. Associated with lecithin, it is also found in 

 the stroma of the red corpuscles of the blood, in leucocytes, in sper- 

 matozoa, in the spleen, in the yolk of birds' eggs, etc. It is 

 questionable, however, whether it actually exists in the free 

 state, and the fact of its constant association with lecithin rather 

 suggests that here also it is primarily present in the protagon 

 molecule. 



Cerebrin is said to have the formula C 70 H 140 N 2 O 13 . Elementary 

 analysis has given the following results : C, 69.08 per cent. ; 

 H, 11.47; N, 2.13; O, 17.32. On decomposition with boiling 

 mineral acids it yields a reducing substance which is commonly 

 regarded as galactose. On oxidation with nitric acid or on fusion 

 with caustic alkali palmitic acid or stearic acid is obtained. If 



