CONSTITUENTS OF FOOD. 93 



XIX. The most recent and exact researches have 

 established as a universal fact, to which nothing yet 

 known is opposed, that the nitrogenized constituents of 

 vegetable food have a composition identical with that 

 of the constituents of the blood. 



No nitrogenized compound, the composition of which 

 differs from that of fibrine, albumen, and caseine, is 

 capable of supporting the vital process in animals. 



The animal organism unquestionably possesses the 

 power of forming, from the constituents of its blood, 

 the substance of its membranes and cellular tissue, of 

 the nerves and brain, of the organic part of cartilages 

 and bones. But the blood must be supplied to it ready 

 formed in every thing but its form, that is, in its 

 chemical composition. If this be not done, a period is 

 rapidly put to the formation of blood, and consequently 

 to life. 



This consideration enables us easily to explain how 

 it happens, that the tissues yielding gelatine or chon- 

 drine, as, for example, the gelatine of skin or of bones, 

 are not adapted for the support of the vital process ; 

 for their composition is different from that of fibrine or 

 albumen. It is obvious, that this means nothing more 

 than that those parts of the animal organism which form 

 the blood, do not possess the power of effecting a trans- 

 formation in the arrangement of the elements of gelatine, 

 or of those tissues which contain it. The gelatinous 

 tissues, the gelatine of the bones, the membranes, the 

 cells, and the skin, suffer, in the animal body, under the 

 influence of oxygen and moisture, a progressive altera- 



