K)OD CONSTITUENTS. SI 



1. Food Constituents and their Functions. The solid 

 ingredients of vegetable food may be classed generally 

 as (1) albuminoids (proteids); (2) fat; (3) carbo- 

 hydrates; (4) salts. Besides these general ingredients of 

 food we have in immature vegetable products a fifth 

 class the amides, which also takes part in animal 

 nutrition. The albuminoids and amides are nitrogenous 

 substances, the other ingredients of food are non- 

 nitrogenous. 



The albuminoids occurring in corn, roots, and other 

 forms of vegetable food, are quite similar in composition 

 to those found in milk, blood, and flesh. From the 

 albuminoids of the food are formed not only the albumin- 

 oids of the animal frame, but also the gelatinoids, the 

 hair, wool, horn, &c., and to some extent the fat. By 

 the combustion of albuminoids in the body heat and 

 mechanical force will also be developed. Albuminoids 

 thus supply in themselves most of the requirements of 

 the animal a statement which can be made of no other 

 food constituent. The albuminoids of food are frequently 

 described as " flesh -formers." 



An animal, even when not increasing in weight, will 

 always require a certain constant supply of albuminoid in 

 its food to replace the waste of nitrogenous tissue which 

 is always going on. The amount of digestible albuminoid 

 required for this purpose is but small ; in the case of an 

 adult man it is not more than forty grams (I '4 oz.) per 

 day. For the requirements of animals see p. 120. 



When the nitrogenous tissues, or the albuminoids con- 

 sumed as food, are oxidised in the body, the nitrogen 

 they contain is not burnt, but excreted in the form of 

 urea. The urea produced is one-third the weight of 



