CHEMICAL COMPOSITION OF NERVOUS CENTRES. 473 



The following is his analysis of the entire encephalon of the 

 foetus at different stages, and that of a child at 6 months : 



Thus the gray substance contains more water than the white, the 

 water being replaced in the latter by fat. The water in the brain 

 of the foetus is also far more abundant than in the adult, the differ- 

 ence being made up by an increase of fat in the latter. The sudden 

 increase of fat for a short time before and after birth, is a fact of 

 much physiological interest. 



The quantity of fat in the brain is found to be constant, within 

 certain limits. It is not diminished in diseases occasioning ema- 

 ciation in other parts, nor is it increased in the lower animals by 

 fattening. It seems to be established that the fat^has important 

 relations to the functions of the brain. Its amount is a little less 

 in old men than in adults in the prime of life. L'Heritier's. analyses 

 also show that it increases from infancy up to adult age. 



In man, other mammalia, and birds, the medulla oblongata con- 

 tains more fat than the cerebellum and the cerebrum. There is the 

 most fat, relatively and absolutely, in the hemispheres of the human 

 brain; next in other mammals, and then in birds, amphibians, and 

 fishes. 



An analysis of the brain-fat shows it to consist of cerebric acid 

 20 to 21 per cent., cholesterine 30 to 33 per cent., and a series of 

 fatty acids constantly varying in composition, and which contain 

 no nitrogen or sulphur. The white substance contains more cere- 

 bric acid and cholesterine than the gray, and consequently less of 

 the other fats. The quantity of cerebric acid seems to diminish as 

 we descend the animal scale, and is less in the foetus and the infant 

 than in the adult. 



Phosphorus is also contained in the brain-fat; except the fatty 

 acids, which solidify at a temperature below 38J (Fahr.). In a 

 man who died at 59 years of age, of Bright's disease, the phospho- 

 rus in the whole brain amounted to 1.68 per cent, of the fat. There 

 was the most in the hemispheres, the cerebellum, and pons Yarolii 

 (1.83 per cent.) ; and the least (1.54 per cent.) in the optic thalami 



