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VICTOE C. MYERS 



reactions, but are distinct chemically. The content of lipoids in the 

 white matter of the brain is very much higher than in the gray matter. 

 A general idea of the distribution of these various substances in human 

 brain tissue may be obtained from the table below taken from Koch. 

 It will be observed that the brain of the adult differs very materially 

 from the child, notably in its higher content of lipoids, particularly 

 cholesterol. With this increase in lipoids there is a corresponding re- 

 duction in protein, extractives and ash. 



COMPOSITION OF THE SOLIDS OF THE HUMAN BRAIN 



Possibly a better notion of the changes in the composition of the 

 brain during growth may be obtained from data given by W. and M. L. 

 Koch on white rats at different age periods. As will be observed well- 

 marked and characteristic chemical changes occur in the rat during its 

 growth which may be correlated with its anatomical differentiation. The 

 principal changes are: "(1) A general decrease in the per cent of the 

 water which is not due entirety to medullation, since the decrease begins 

 before medullation; (2) a diminution in the relative per cent of protein 

 in the total solids due to the formation of a large amount of lipoid matter ; 



(3) the lipoids which appear coincident with medullation and of which 

 the development is pari passu with medullation are the cerebrosids and 

 phosphatids. These, therefore, are chiefly found in the medullary sheaths. 



(4) There is a great outburst of phosphatid formation at the very be- 

 ginning of medullation. The phosphatids are present, therefore, in the 

 cells as well as the sheaths." 



The chemistry, so far as known, of the various lipoid substances 

 present in brain is of considerable interest. From the studies of Posner 

 and Gies, and others, it is apparent that the nitrogenous phosphorized 

 substance isolated by Liebreich and named "protagon" is a mixture. 



Phosphatids. The best examples of the phosphatids are lecithin and 

 cephalin. Recently Levene and West have shown that it is possible to 

 prepare perfectly pure lecithin. The lecithin molecule is known to be 

 made up of two molecules of fatty acid, one of glycerol, one of phosphoric 

 acid and one of the base, cholin. The lecithin of brain tissue appears to 



