CHEMICAL CHANGES IN HUMAN BRAIN 457 



Under the heading of organic phosphorus is included a number 

 of comparatively simple compounds of phosphorus with organic 

 radicles. There is no definite separation of this group from the 

 following one (Emmett and Grindley, '06). It is representative 

 of the amount of protein metabolism and bears a definite relation 

 to the two colloidal forms of phosphorus mentioned above. 



Inorganic phosphates are also a measure of rate of activity. 

 In fact, the sum of these last two forms the best criterion of rate of 

 phosphorus metabolism. It is worth noticing that in terms of 

 percentage of total phosphorus the amounts of colloidal phos- 

 phorus compounds are increasing with growth, while those of the 

 crystalloidal forms are decreasing (table 11). In fresh tissue the 

 percentage of extractive phosphorus increases slightly, then de- 

 creases to a certain extent; but these small variations from a 

 constant may not be significant. The figures, however, indicate 

 rather definitely that these simpler forms of phosphorus do not 

 closely follow the change in percentage of water, as one would 

 expect if the quantity of fluid determined the amount of ex- 

 tractives. From table 11 it is evident that extractive phos- 

 phorus, like other extractives, markedly decreases in the per- 

 centage of total solids. 



Comparison of forebrain, cerebellum, and brain stem 



In the adult brain the cerebellum contains the largest per- 

 centage of water, the forebrain slightly less, the brain stem least. 

 A high percentage of solids indicates slower but more highly 

 dfferentiated metabolism; therefore the cerebellum acts fastest, 

 while the brain stem is most stereotyped. During growth the 

 rate of increase in the percentage of solids is in the following 

 order, brain stem (table 4), forebrain (table 1), and cerebellum 

 (table 7) ; this is, of course, to be expected. 



In the stem the phosphatids are in larger amounts (table 5) 

 and are probably laid down earlier than in the other two divisions 

 of the brain. The cerebellum contains the smallest amount of 

 this group of constituents (table 8) , indicating that it is probably 

 less highly specialized than other parts. 



