250 PROCEEDiyGS OF THE NATIONAL MUSEUM. 



The hardening of small mammal and bird brains was effected much 

 like that of the larger specimens. In hardening fatal human brains, 

 the best results were obtained h\ the aid of stronger alum solutions. 



The color of the brain (except so far as it ma}' be due to hemoglobin, 

 which is bleached) was affected but little by any of the solutions em- 

 ployed. Sodium chloride produced a lighter color or bleaching of the 

 tissues; alum a slighth' grayish tinge of the surface. AUnn was more 

 effective tiian salt in showing the differentiation of the gray and 

 white matter. 



(2) ^^'ith all the care exercised, the ratio of change in an}' given series 

 in which the same preservative had been used was not uniform. A 

 large portion of the irregularity must be attributed to the physical 

 status, and some probably to the chemical condition of the organ. 

 "When the two halves of any brain were treated in the same preserva- 

 tive, the results were always much alike. 



The physical condition of the brain includes its size and the quan- 

 tity of blood or other liquids it may contain. The size of the brain has 

 been found in general to have a pronounced influence upon the weight 

 and vokune changes in the organ. The larger the brain, the smaller 

 the per gram changes, and the opposite. While there are individual 

 exceptions, the cases conforming to the rule (see detail tables) are too 

 numerous to leave any doubt on this point. What the causes of this 

 phenomenon are is not yet clear, though presumably the larger brains 

 have a tirm(M- structure — that is, could better resist absorption" — and 

 the very small brains are of necessity preserved in relatively nuich 

 larger quantities of fluid, which may aid solution. It is possible that 

 it is mainly if not entirely the size which accounts for the differences 

 between the changes in three principal series of brains — those of human 

 beings, of mammals, and of birds — but this needs further experimenta- 

 tion before a flnal decision can ])e obtained. 



The degree of brain congestion nuist be a factor affecting the brain 

 changes, hut not enough specimens came to hand to throw much light 

 on this i)()int. Theoretically, a congested ])rain ought to gain less and 

 lose more than a normal one. in any preservative. Higher degrees of 

 congestion, not unconnuon in human specimens, are rare in other 

 larger maninials and are practically never met with in the smaller 

 animals. 



Besides the differences in the changes of various brains in the same 

 preservative, accountable for l)y marked ditterences in the physical 

 characteristics of the organ, others are met with harder to explain. 

 In some instances, as with Lepm ctmicultts, Cathartes aura, and a few 

 others (see detailed lists), there is a suggestion that the difference 



"In a number of instances the hemispheres of small brains, preserved in weak for- 

 malin solution (1 ur 2 per cent) in the laboratory, have burst through the great 

 absorntion. 



