METABOLIC ACTIVITY OF NERVOUS SYSTEM 



365 



We shall discuss this subject more fully in connection with 

 the studies on the parts of the central nervous system. 



The graphic representation of the content of non-protein 

 nitrogen is given in chart 1. 



50 



100 



150 



900 



250 



300 



350 



400 



Chart 1 Showing the number of milligrams of non-protein nitrogen per gram 

 of the dried brain at different ages. The chart shows also the proportional 

 value of organic extractives together with inorganic salts in the brain of the 



albino rat, as determined by W. Koch and M. L. Koch ('13). Non-protein 



nitrogen, X organic extractives and inorganic salts. 



One striking relation which is well shown in the chart is the 

 rapid fall of the content of non-protein nitrogen within the first 

 fifteen days of life. At the end of this period the rate of reduc- 

 tion becomes much less till the animal reaches about one hun- 

 dred and twenty days. After one hundred and twenty days the 

 subsequent changes are almost negligible. The general appear- 

 ance of the curve is similar to that for the percentage of water 

 in the brain at different ages (Donaldson, '15). One difference 

 between these two cases lies in the fact that the non-protein 



