CHEMICAL CHANGES IN HUMAN BRAIN 



449 



Whole brain: Weights of divisions in grams 



Whole brain. 

 Forebrain. . . 



Left 



Right 



Cerebellum. . 

 Brain stem. . 



ADULT 



65 

 TEARS 



1297.9 



1075.0 



535.0 



540.0 



145.4 



77.5 



^ See section on Limitations for explanation. 



* Analyzed together because of small amounts of each. 



DISCUSSION OF RESULTS 

 Water and total solids 



The water determinations show that though the absolute 

 amount increases (table 12, fig. 1), the percentage of this constit- 

 uent decreases continually (table 10) until growth is completed. 

 The relative amount of water present is an indication of the rate 

 of activity. Water, like the inorganic salts and the simpler 

 organic substances (table 10), decreases relatively rather reg- 

 ularly with the approach to adult condition and its decrease in 

 rate of metabohsm. 



The percentage of total solids of course varies inversely with 

 that of water. The increase is largely due to the formation of 

 the colloidal substances. They increase in absolute amounts 

 (table 12, fig. 1) and in percentage (table 10), while the simpler 

 molecules, as a rule, decrease in percentage, but increase in 

 absolute quantity. It will be noticed from table 13 and figure 2 

 that the solids are formed most rapidly soon after birth; at least 

 0.5 grams a day are then being added. This coincides with the 

 period of most rapid myelination. 



It does not necessarily follow that this is the time of greatest 

 protoplasmic activity, because under other conditions the 

 products of the reaction may be removed, while during the 

 period of myelination a part may form the sheath. 



It needs to be remembered that the substances produced in 

 myelination are not to be thought of as active protoplasmic 



