420 JAMES STUART PLANT 



Cerebellum 5.8 per cent 



Stem 5.0 per cent 



Cerebrum 3.9 per cent 



Olfactory bulbs 1 .5 per cent 



Average of whole brain 4.3 per cent 



With the exception of the cerebellum, the percentage of salts 

 deposited is in direct relation with the proportion of myelin in 

 the part involved. As none of the parts were washed, it may 

 well be that the interstices of the cerebellum were the site of 

 large deposits of salts, a physical factor which may account for 

 this anomalous result. 



CONCLUSIONS 



General reaction of the brain to Miiller's fluid, or type curves. 

 The brain of the albino rat undergoes a typical change when 

 'fixed' in Miiller's fluid (2.5 per cent potassium bichromate and 

 1 per cent sodium sulphate). There is a rapid increase in 

 weight followed by a slow, steady loss until at the seventy-five- 

 day weighing the brain weighs 20 to 30 per cent more than when 

 fresh. 



Factors affecting this reaction, or components of the type 

 curve. 



1. Age is the main condition controlling this reaction to 

 Miiller's fluid. The brains of older rats gain more and retain 

 this higher relative gain throughout the seventy-five days. 



* 



2. Initial brain weight, or size, is the condition of next impor- 

 tance. As between brains of like age the lighter brains gain 

 more during the earlier part of their stay in Miiller's fluid. This 

 difference is gradually lessened, and it disappears at the seventy- 

 five-day weighing. 



Thus, while age and initial brain weight are highh^ correlated, 

 they constitute factors which, when taken alone, influence in 

 opposite ways the reaction of the brain to Miiller's fluid. The 

 early greater increase of the smaller brain of two rats of the 

 same age may be due to one or both of the following factors: 



a. If we consider the brain as a sphere and the fluids as pene- 

 trating at a fixed rate, then in the smaller brain a slightly greater 



