CHEMICAL CHANGES IN HUMAN BRAIN 455 



remember that it may be more accurate to leave the sheath sub- 

 stances out of the reckoning. The calculations would then be 

 based on the assumption that but three-fifths of total solids are 

 directly concerned. 



Sulphur compounds 



By estimating sulphur in the various fractions we obtain in- 

 formation about the relative amounts of several important brain 

 compounds. The lipin sulphur is a measure of the amount of 

 sulphatid, and is therefore largely concerned in sheath devel- 

 opment. In consequence it obtains a maximum rate of forma- 

 tion at about three months of age. Protein sulphur represents 

 the amount of cystin in protein combination. Cystin is present 

 in much smaller amounts in the nucleoproteins of the brain than 

 in neurokeratin. So protein sulphur gives us a rough estimate 

 of the amounts of neurokeratin being formed. It will be noticed 

 that this form of sulphur follows very closely myelin formation 

 (table 10). Neutral sulphur may represent an intermediate 

 oxidation product of cystin or possibly taurin; an increase in 

 this form might indicate a decreased oxidative ability in the cells 

 (W. and M. L. Koch, '13). Of the total sulphur, neutral sulphur 

 forms a greater portion in the younger tissue, while the portion 

 of protein sulphur increases with age. The inorganic sulphates 

 are the final sulphur oxidation products. They remain rather 

 constant in percentage amounts (table 11). This may be due 

 to the fact that, they are readily eliminated from the cell. Total 

 sulphur increases in percentage of fresh tissue until adult age, 

 then remains rather constant. The maximum addition, of about 

 3 mg. per day, takes place at about three months of age (table 13). 



Phosphorus compounds 



The amount of phosphorus in the lipins is used to determine the 

 amount of the phospho-lipins. It is added most rapidly at birth 

 (table 13, fig. 2) (at least 3.5 mg. per day), but like most of the 

 other constituents, its rate of addition per unit of reaction sub- 

 stances is greatest in the youngest tissue (tables 14 and 15, 

 fig. 3). 



THE JOURNAL OF COMPARATIVE NECROLOGT, VOL. 30, NO. 5 



