NOTES TO VOL. III. 555 



7- In man, other mammals, and birds, the medulla oblongata 

 contains the largest amount of fat. 



8. The quantity of fat in the hemispheres is both relatively 

 and absolutely greater in man than in the other mammals, and in 

 the latter than in birds. 



9. The whole quantity of brain-fat in old men is a little less 

 than that in adults in the prime of life. 



10. The water and solid constituents (the fat not being included) 

 fall and rise in their amount in all classes of animals with the aug- 

 mentation or diminution of the fat, the albuminous matters being 

 liable to the greatest variations. 



11. It is not definitely established that the brain in mammals 

 contains a larger mean quantity of water than the human brain ; 

 it would appear as if in this class of animals the smaller quantity of 

 fat is compensated for by the albuminous substance rather than by 

 water. 



12. In birds, on the contrary, the amount of water in the brain 

 is unquestionably larger than man or other mammals. 



Von Bibra believes that the analyses, from which the preceding 

 conclusions are drawn, establish beyond all question the importance 

 of the fat in relation to the functions of the brain. 



II. The brain-fats seem to have been submitted by him to a very 

 careful investigation. The following are his chief conclusions. The 

 brain-fats consist of cerebric acid and cholesterin, and of a series 

 of fatty acids which possess very different properties and very diverse 

 fusing points. These fatty acids are not the same in different 

 brains even of one and the same species ; and it would seem pro- 

 bable that in the living organism they are undergoing perpetual 

 decomposition, passing into one another, and taking a share in the 

 cerebral functions. They contain 110 nitrogen or sulphur, and those 

 which solidify below 12*5 C., contain no phosphorus. 



His cerebric acid agrees very well with the acid described by 

 Fremy : von Bibra however finds as a mean of five analyses only 

 0'52-g- of phosphorus (the extremes being 0'49 and 0'55j), whereas 

 Fremy fixed this constituent at 0'9f. He found that in adult men 

 the brain-fat contains 20 or 2 If of cerebric acid, and from 30 to 

 33 of cholesterin, while the remainder is made up of the above- 

 noticed fatty acids and their salts. 



The cerebric acid is rather more abundant in the brain of man 

 than in that of the other large mammals. 



The grey substance of the brair contains the least cerebric 



