366 



S. HATAI 



nitrogen shows its greatest reduction within the first fifteen 

 days, while in the case of water, the approximate end of a rapid 

 fall is not reached until about twenty-five days after birth. It 

 is interesting to note that the percentage of water in the \dsceral 

 organs also falls off rapidly, while the ligamentous skeleton 

 (Lowrey '13) shows the water content similar in its time relations 

 to that of the brain. Whether the difference noted between the 

 fall in the percentage of water and the fall in the non-protein 

 nitrogen in the brain has any important physiological meaning, 

 or is merely due to a comparatively small number of observations 

 made on the non-protein nitrogen, is not entirely clear, though 

 the latter explanation does not seem very probable. 



ORGANIC EXTRACTIVES AND INORGANIC SALTS IN THE BRAIN 



The so-called 'extractives' consist of both nitrogenous and 

 non-nitrogenous fractions. My present determinations were 

 exclusively made on the nitrogenous fraction. Nevertheless it 

 is of interest to determine whether or not the non-nitrogenous 

 fraction also varies with the age of the rat in a way similar to 

 that of the nitrogenous fraction. The data given by W. Koch 

 and M. L. Koch ('13) were utilized to test this point, and are 

 ^ven in table 2, and seem to show such a concomitant variation. 



TABLE 2 



Showing the quantitative relations existing between the total dry substance of the 

 brain and the organic extractives plus the inorganic salts, in the albino 

 rat at different ages. W. Koch and M. L. Koch 1913 



AGE IN DAYS (aLBINO RAT) 



40 



120 210 



Dry weight of one brain in milligrams (A).... 

 Organic extractives and inorganic salts in 



milligrams (B) 



Milligrams of (B) per 100 milligrams of (A) (C). 

 2.121 percent taken from (C) gives 



26 



4.65 

 17.9 

 14.1 



107 



16.16 



15.1 



12.9 



224 



32.6 

 14.5 

 11.4 



281 



41.7 

 14.8 

 11.7 



347 



33.8 

 9.7 

 7.6 



365 



35.8 

 9.8 



7.7 



^ 2.12 per cent were taken off from the value given in 'C in order to equalize 

 the two initial values (one day old) ; one given by these data, and the other the 

 number of milligrams of non-protein nitrogen per gram total brain solids for a 

 one day old rat (table 1, column (i) ). 



