HYDROLYSIS PllODUCTS OF CEREBROSIDES 499 



volumes of water without removal of the precipitate which forms. After 

 acidification with sulfuric acid, the fatty acid is extracted with diethyl 

 ether. After removal of the ether by distillation, the acid residue is dis- 

 solved in 15 volumes of alcohol; the hydroxj^-acids are precipitated from 

 the boiling solution by the addition of a hot saturated methanolic solution 

 of magnesium acetate. The precipitate which forms immediately in the 

 hot solution is the magnesium salt of hydrox3aiervonic acid. It is filtered 

 from the hot solution and the hydroxynervonic acid is obtained from it by 

 the general method employed above. 



When the filtrate is cooled, after removal of the magnesium hydroxy- 

 nervonate, a small amount of a magnesium salt precipitates at room tem- 

 perature; this is filtered off and discarded. The alcoholic solution is 

 mixed with an equal volume of water acidified with sulfuric acid. The 

 fatty acid set free is extracted with petroleum ether. The latter fraction is 

 then washed with water and the nervonic acid present is recovered by re- 

 moval of the petroleum ether by distillation. 



(c) Calculation of Amount of Each Fatty Acid. The amount of unsatu- 

 rated fatty acids can be calculated from the iodine number of the crude 

 fraction of the unsaturated fatty acids worked up in (6). In the case of 

 the hydroxynervonic acid fraction, the remaining fatty acid can be con- 

 sidered to be cerebronic acid. This is added to the amount of the cerebronic 

 acid isolated under (a). The value for the saturated acid present in the 

 nervonic acid fraction is much smaller; the acid cannot be considered as 

 lignoceric acid without further analysis.* 



(-5) Carbohydrate Component 



The sugar component of cerebrcsides may be either galactose or glucose. 

 Thudichum,^^^'"^ who originally discovered that a sugar is set free when 

 the cerebroside is hydrolyzed, believed that the carbohydrate was an 

 entirely new hexose, for which he coined the term "cerebrose." However, 

 Thierfelder'*''* and almost simultaneously Bro^^Tl and Morris'"'^ proved that 

 cerebrose is identical with c?(+)-galactose. The fact that the sugar in 

 some cases may be glucose instead of galactose has only recently been 

 demonstrated.^^" 



Galactose may best be prepared from phrenosine after hydrolj'sis with 

 7% aqueous sulfuric acid by heating on a water bath over a prolonged 

 period. The insoluble material is filtered off, the excess sulfuric acid is 

 removed with baryta, and the excess barium with carbon dioxide. After 

 concentration and filtration, galactose separates in crystalline form from 

 the filtrate. •'^^ The carbohydrate has been characterized as galactose be- 



«^ 11. Thiorfeldcr, Z. physiol. Client., 14, 209-210 (1890). 



^65 11. T. Brown and G. II. Morris, J. Chem. Soc, 57, 57-59 (1890). 



