176 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



The substance, sphingomyelin, is also found in tissues, but in larger 

 quantities in brain substance. It contains phosphorus like lecithin and 

 kephalin, but not glycerol. Its constituents are two fatty acids, 

 choline, sphingosine and phosphoric acid. These three substances 

 form the group of phosphatides. Sphingosine is an unsaturated com- 

 pound and contains two hydroxyl groups : 



C 12 H 25 . CH = CH . CHOH . CHOH . CH 2 . NH 2 . 



Brain tissue contains sphingomyelin and the two cerebrosides, 

 phrenosin and kerasin. This mixture constitutes protagon. The 

 cerebrosides do not contain phosphorus. They are composed of the 

 base sphingosine, galactose and a fatty acid, the sphingosine in com- 

 bination with the galactose in the form of a glucoside and in com- 

 bination with the fatty acid in the form of an acid amide : 



galactose sphingosine phrenosinic acid (C25H 50 O3). galactose sphingosine lignoceric acid (CvtHtfOz). 



v_ . ^ ' v _^ , 



phrenosin. kerasin. 



These compounds have also been isolated from other organs. A full 

 account of these substances is given in Maclean's monograph. 



Properties. 



Fats and oils, waxes and lecithin have solubilities like the fatty 

 acids. They are not soluble in water and are not soluble in dilute 

 cold sodium hydroxide. 



On warming, the fats melt and become oils. They have fairly 

 definite melting-points. Fats and oils are not easily soluble in 

 alcohol, but dissolve readily in ether, ligroin, carbon disulphide, etc. 



Lecithin is easily soluble in cold absolute alcohol, in ether and 

 other solvents. It is nearly insoluble in acetone, and may be pre- 

 cipitated from a concentrated ethereal solution by the addition of 

 acetone. Kephalin is not soluble in alcohol. The cerebrosides dis- 

 solve in hot alcohol, acetone, benzene, but not in the cold solvent. 

 They are insoluble in ether. 



Extraction of Fats, etc. 



The fats are contained in animal and vegetable tissues mixed with 

 protein and carbohydrate. Three methods are in use for their separa- 

 tion. The oldest and simplest method consists in melting out the fat 

 from the tissue by simply placing it in a suitable receptacle of muslin 

 or cloth in a warm room ; the fat melts and runs out leaving the re- 

 mainder of the tissue behind. The most modern method consists in 

 pressing out the fat in a hydraulic press ; this is the method most fre- 

 quently employed for obtaining the oils from vegetable seeds. The third 

 method consists in extracting the fat by means of suitable solvents, 

 such as benzine, carbon disulphide. Alcohol and ether are not usually 

 employed for this purpose, but they are generally used if an estimation 

 of fat in a tissue be required. For food the fat or oil is pressed out; 

 for soap making and other purposes the residue is extracted. 



