392 THE NERVE-TISSUE. 



the substance is dissolved in concentrated sulphuric acid, the 

 solution gradually assumes a purplish-red color, which changes 

 to violet, and finally to brown. On adding an equal amount of 

 water and boiling, a flocculent precipitate appears, which is known 

 as cetylidj and is said to have the composition C G4 H 120 O 75 or 

 (C 16 H 31 O 2 ) 3 .[C 16 H 18 (OH) 3 ]. This substance supposedly represents 

 about 85 per cent, of the entire weight of the cerebrin. It 

 is soluble in water, in hot alcohol, and especially in ether and 

 chloroform. On fusion with caustic alkali, cetylid yields methane, 

 hydrogen, and palmitic acid. 



Pure cerebrin is a colorless substance which occurs in the form of 

 a crystalline powder, consisting of microscopical globulites. It is 

 soluble in warm acetone, acetic ether, benzene, and boiling alcohol, 

 but is insoluble in sulphuric ether, even at its boiling-point ; with 

 chloroform it forms an emulsion. In cold water it is likewise 

 insoluble. In boiling water it swells to a certain extent, like starch 

 paste. It melts at 177 C., but is decomposed long before with 

 the development of a yellow or brownish color. Its reaction is 

 neutral. 



Isolation. Cerebrin can be obtained either from protagon after 

 the separation of .the latter or directly from the brain by decompos- 

 ing its antecedents with baryta-water. To this end, the material 

 after being freed from its membranes and blood is stirred with 

 baryta-water, and brought to the boil. The insoluble portion is 

 then pressed out and repeatedly extracted with alcohol by boiling. 

 The extract is filtered while still hot, when on cooling to C. ? 

 the cerebrin separates out in impure form. It is freed from choles- 

 terin and fats by skaking with ether, and purified by repeated solu- 

 tion in hot alcohol and subsequent cooling, until jelly-like pre- 

 cipitates, which are referable to homocerebrin or encephalin, are no 

 longer obtained. 



With this method, however, a considerable portion of the cerebrin 

 is decomposed, and Kossel has accordingly suggested that the 

 protagon be first extracted and subsequently decomposed. To this 

 end, the substance is dissolved in methyl alcohol, and is treated with 

 a hot methyl alcoholic solution of barium hydrate. The mixture is 

 warmed for a few minutes on a water-bath, and then allowed to 

 cool. The resulting precipitate contains the entire amount of 

 cerebrin which can be obtained, and represents 50 per cent, of the 

 original quantity of protagon. It is filtered off, suspended in water, 

 and freed from barium by a current of carbon dioxide. The insolu- 

 ble residue contains the cerebrosides, which are now extracted with 

 hot alcohol and isolated by fractional crystallization. 



Homocerebrin (Kerasin). The formula of homocerebrin is 

 given as C 70 H 138 N 2 O 12 , and the substance could hence be regarded as 

 an anhydride of cerebrin. In the dry state it occurs as a wax-like 

 mass, which can be pulverized only with difficulty. From its solu- 

 tion in alcohol and boiling ether it separates out in aggregates of 



