376 S. HATAI 



or myelin? Mathews ('16) considers that the function of myehn 

 is probably nutritive and certainly there is some indirect evi- 

 dence favoring this view. I have however at the present moment 

 no direct evidence on the basis of which to discuss this question, 

 but it is my hope to extend my research into this obscure field 

 in the future. 



CONCLUSIONS 



1. The number of milligrams of non-protein nitrogen per gram 

 of solids decreases rapidly in the course of the first fifteen days 

 of life. After the fifteenth day, the approximate time when 

 myehn appears, and up to about one hundred and twenty days, 

 the rate of decrease becomes much slower. After one hundred 

 and twenty days the change is hardly noticeable. This decrease 

 is interpreted as the result of the accumulation of myelin, a sub- 

 stance which probably has no direct relation to the nitrogenous 

 metabolism (table 1 and chart 1). 



2. The relative amount of organic extractives and inorganic 

 salts to the total solids changes with advancing age in a way 

 similar to the non-protein nitrogen. This is interpreted as 

 meaning that the change in the non-nitrogenous organic extrac- 

 tives is similar to that in the nitrogenous fraction (table 2 and 

 chart 1). 



3. The number of milligrams of non-protein nitrogen per 100 

 grams of fresh tissue is much less in the brain than in other 

 organs so far examined (testes, liver and kidneys). The nitro- 

 gen values given by the amino acids, the urea and the ammonia 

 are very similar to the values given by several other organs and 

 tissues of other mammals (tables 3 and 4). 



4. Although the amount of nitrogen given by the non-pro- 

 teins, the amino acids, the urea and ammonia in relation to the 

 solids is higher in the cerebellum and cerebrum than in either 

 the stem or the spinal cord, these nitrogen values become con- 

 stant in all the four parts when they are computed in relation 

 to the protein nitrogen. This is interpreted to mean that the 

 nitrogenous organic extractives are intimately related with the 



