CARBOHYDRATE ESTERS 91 



of a saponin; it is, however, devoid of lytic action upon the red blood- 

 cells themselves. 



The glucosides in the brain, the Cerebrosides, occur in complex fatty 

 compounds which yield the free glucosides, Phrenosin and Kerasin oil 

 partial hydrolysis. They also exist in part preformed in brain-tissue, 

 or at any rate can be directly extracted therefrom by solvents such 

 as pyridine or hot alcohol containing benzole or chloroform. These 

 substances are not confined to nervous tissue but are also present in 

 small amounts in the kidney and liver and probably in other organs as 

 well. They also occur in the yolks of eggs. 



The cerebrosides are nitrogen-containing substances which are 

 hydrolyzed by acids, yielding fatty acids, galactose, and a nitrogenous 

 base, Sphingosine, which is a diatomic amino-alcohol containing unsatu- 

 rated linkages: 



: CH.CHOH.CHOH.CH 2 NH 2 



The fatty acid which is yielded by Phrenosin is a hydroxy-acid, 

 Cerebronic Acid, C25H 5 oO 3 , while Kerasin yields Lignoceric Acid, C^JH^sC^. 

 The two cerebrosides differ furthermore in their solubilities, phrenosin 

 being almost insoluble in boiling acetone, while kerasin is readily 

 soluble. Both cerebrosides are insoluble in water or in ether, but they 

 dissolve in hot alcohol, from which they crystallize in needles or plates 

 on cooling. Solutions of phrenosin are dextrorotatory, those of kerasin 

 being levorotatory. 



With sulphuric acids the cerebrosides yield, first a yellow, and later 

 a purple-red coloration. In the presence of cane-sugar and sulphuric 

 acid, they yield a purple coloration immediately. This reaction is 

 attributable to the sphingosine radical. 



Cerebrosides are absent in the brains of fetal animals, but with the 

 advance of medullation they appear in abundance. It is therefore 

 assumed that the cerebrosides are constituents originating in medullary 

 sheaths rather than in the axons or nerve-cells. 



THE CARBOHYDRATE ESTERS. 



Phosphoric acid esters of d-glucose and d-ribose occur among the 

 products of the partial hydrolysis of nucleic acids. They will fall under 

 more extended consideration in a later chapter. 



Sulphuric acid esters, the Glucothionic Acids have been found by 

 Levene and Mandel in a variety of animal tissues, the nature of the 

 carbohydrate radical is not yet established. 



A sulphuric acid ester of an amino-polysaccharide, Chondroitin- 

 Sulphuric Acid, CigH^NOisHSCX occurs in important amounts in bones 

 and other sclerous tissues and also in the walls of the great arteries 

 and in certain pathological tissues. It is a normal constituent of urine 

 in very small amounts. It is soluble in water, yielding levorotatory 



