154 DIGESTION. [CHAP. xxii. 



for this purpose, a special supply of carbonaceous material must be 

 furnished to the blood and this is derived from the non-azotized 

 alimentary substances. We prefer, then, the terms lately proposed 

 by Dr. R. D. Thomson, namely, calorifacient for the non-nitrogen- 

 ized substances, nutritive for the azotized matters. 



It is proper to notice that azotized matters may be calorifacient, 

 inasmuch as they contain a large quantity of carbon ; and it is 

 known that large tribes of men live on animal food alone. A 

 large number of North American Indians, according to Cattlin, 

 live almost exclusively on the flesh of the buffalo, the only non- 

 azotized food which they obtain being the fat belonging to it 



In determining the nature of the diet to be furnished in order to 

 preserve man in a healthy state, care must be taken to provide for 

 the calorific as well as the nutrient function ; and hence the ad- 

 mixture of a certain quantity of non-azotized food is needed for the 

 former function. In the cold northern climates, the natives in- 

 stinctively feed on fat and oily food, which contains a large per- 

 centage of carbon; while the natives of the warm south feed on 

 fruits, which, as Liebig says, contain no more than twelve per cent, 

 of carbon. Milk, the food of the young, in whom the produc- 

 tion of heat ought to be most active, contains, according to Dr. 

 Thomson, two parts of calorifacient for one of nutritive matter. 

 Eggs also contain nutritive matter in a concentrated form, consist- 

 ing chiefly of pure albumen, to which a considerable quantity of 

 calorifacient matter is added in the oleaginous yolk. The accumu- 

 lation of these substances, as a natural provision for the nourish- 

 ment of the young, whilst yet under the sole guidance of the purest 

 instinct, or, as in the egg, where the nutrient matter is directly ab- 

 sorbed by the tissues of the embryo, affords the surest indication 

 that a compound food, consisting of such elements, is necessary for 

 perfect nutrition at this period of life. As age advances, or the 

 generation of animal heat becomes less active, the quantity of calo- 

 rifacient food required is less, and that of the purely nutrient food 

 more. 



Experience justifies the conclusion, to which our reasoning on 

 these points leads, namely, that in the temperate climates the pro- 

 per nutrient materials for infancy and childhood are milk, saccharine 

 and amylaceous substances, the latter being combined with gluten ; 

 and that to these must be added a certain amount of gelatine, 

 albumen, and fibrine, when the growth of the child and the more 

 active play of its nervous and muscular systems calls for a further 

 supply of nitrogenized food. In adult life, azotized substances are 



