416 JAMES STUART PLANT 



A further study was made of fifty-nine brains arranged accord- 

 ing to increasing brain weight but without regard to sex or litter. 

 In table 4 these are arranged according to initial brain weight in 

 three age groups. Within these groups two phenomena are 

 apparent (shown in the averages under the vertical column, 

 'Percentage difference from the following value'). These are the 

 early greater gains for the lighter brains (this does not hold 

 clearly for the ten brains of the youngest group where there is 

 practically no difference); and the fact that at the seventy-five- 

 day weighing the lighter brains show relatively a less percentage 

 of increase than they do at the twenty-four-hour weighing. 

 Since these facts are just those which determine the curve when 

 brains of rats of the same age, sex, and litter are compared, we 

 may conclude that in the reaction of the brain to Miiller's fluid: 



1. Sex is negligible. 



2. Inherited composition is negligible. 



3. Approximate similarity of ages (the range being limited) 

 may be considered as having the same effect as though the ages 

 were identical. 



The data on the percentage' of water — in the last column of 

 table 4 — will be discussed later. 



A group of four brains — all belonging to young rats — was sub- 

 jected to an additional procedure. The brains, immediately 

 upon removal, were separated into cerebrum, cerebellum, stem, 

 and olfactory bulbs. Each part was then treated as were the 

 whole brains of the other series. The data are given in table 5 

 in this way, that that percentage of the whole brain weight 

 represented by the weight of each part at each weighing is re- 

 corded. The figures for the four brains show but slight varia- 

 tion, and table 5 therefore presents onl}^ the averages of the four. 

 The relative weights of the various parts undergo considerable 

 change in Miiller's fluid, but this change is mainly consummated 

 in the first twenty-four hours. Thus we may assume from this 

 study that, while the relations of the various parts are altered in 

 the fixing solution, the length of time, after the first twenty-four 

 hours, during which the parts are subjected to this treatment, is 

 a matter of minor import. 



