37 2 PHYSIOLOGICAL CHEMISTRY 



is said by some investigators to yield cerebrin and the decomposition 

 products of lecithin. It has been shown by Posner and Gies 1 as well 

 as by Rosenheim and Tebb 2 that protagon is a mixture and has no 

 existence as a chemical individual. Koch 3 reported data obtained 

 from purified preparations which indicate that protagon contains at 

 least three substances: a "phosphatide containing cholin, a cerebro- 

 side containing sugar, a complex combination of a cholin-free phos- 

 phatide with a cerebroside to which an ethereal sulphuric acid group 

 is attached." On the basis of his data, he believed the term pro- 

 tagon to have no chemical significance. He proposed the term sul- 

 phatide. Koch's preparation analyzed as follows (per cent) : 



Choline Sugar Nitrogen Phosphorus Sulphur 



i.o 12.0 2.3 1.7 i. 9 



He suggested the following structure: 



O 



II 



Phosphatide S Cerebroside 



grouping grouping 



O 



Kephalin is the third member of the group of phosphorized fats. 

 It is precipitated from its acetone-ether extract by alcohol. It contains 

 about 4 per cent of phosphorus and has been given the formula C42Hy9- 

 NPOis. Kephalin may be a stage in lecithin metabolism. 



The cerebrosides are substances containing nitrogen but no phos- 

 phorus, and are important constituents of the white matter of nervous 

 tissue. Certain ones have also been found in the spleen, pus, and in egg 

 yolk. They may be extracted from the tissue by boiling alcohol and are 

 insoluble in cold alcohol, cold and hot ether, and in water and dilute 

 alkalis. The cerebroside termed cerebrin is a mixture containing phre- 

 nosin (pseudo-cerebrin or cerebron), a body yielding the carbohydrate 

 galactose on decomposition. 



Cholesterol, one of the primary cell constituents, is present in fairly 

 large amount in nervous tissue. It occurs in two forms, i.e., free and 

 combined as an ester. It is claimed 4 that 99 per cent of the choles- 

 terol of brain tissue (boy) it in the free state. It is a mon-atomic 

 alcohol containing at least one double bond and possesses the formula 

 C27H 46 OH or C 2 7H 43 OH. There is still some uncertainty as to the 

 exact structure of cholesterol. It may possess a terpene structure. It 



1 Posner and Gies: Journal of Biological Chemistry, i, 59, 1905-06. 



2 Rosenheim and Tebb: Journal of Physiology, 36 and 37, 1907-08. 



8 Koch: Journal Biological Chemistry, n, March, 1912, Proceedings. 

 4 Lapworth: Jour. Path. Bad., 1911, p. 256. 



