ALBINO RAT ERAIN IN MULLER's FLUID 421 



proportion of the brain will be penetrated — that is, swollen by 

 the fixing fluid — at any given instant in the early part of the 

 reaction. This would give a more rapid enlargement in the 

 smaller brain. 



6. The smaller braili has a higher percentage of water which 

 might make diffusion more rapid. If this is a controlling factor, 

 the matter of a higher percentage of water must be of more 

 immediate importance than is that of a lesser percentage of 

 myelin. 



3. Approximately similar age (the range being limited) has 

 nearly the same determining value as equality of age. 



4. Sex is a negligible factor, as is also inherited composition 

 (relationship within a given strain). 



FINAL WATER RELATIONS 



The increase in weight is due mainly to the taking up of water, 

 but the percentage of salts deposited in the fixed tissues is much 

 greater than that in the fixing fluid. With the exception of the 

 cerebellum, the deposition of salts is proportional to the myelin 

 present in the part of the brain. 



RELATION OF RESULTS 



The curve of reaction of 'control' brains to Mliller's fluid is 

 evidently of such constancy in character as to make it a satis- 

 factory criterion for a judgment as to alterations produced in 

 the brain by various experimental procedures. It seems that 

 in problems involving changes not available to such microscopic 

 or analytical tests as we have, this reaction might furnish a 

 valuable means of study. It appears from the foregoing results 

 that when tests are made for the experimental modification of 

 the response of the brain to Mliller's fluid, it is necessary to have 

 the test and control brains of the same age and, in those cases in 

 which the brains differ in weight, to allow sufficient time for the 

 compensation of this difference. 



