78 ANIMAL PHYSIOLOGY. 



required for an adult man about 40 ounces of so-called solid 

 food, yielding 22 or 23 ounces when evaporated to dryness, 

 and from 50 to 80 ounces of water. 



50. The aliment required by the body consists of organic 

 food, salts, and water. The reason why water is required in. 

 larger proportion in our aliment than that in which it exists in 

 the tissues, is that, by processes of filtration and evaporation, 

 the body is constantly losing water by the skin, the kidneys, 

 and the lungs, additional to what is produced by waste of 

 tissue. Common salt or chloride of sodium, on account of its 

 great solubility and the ease with which it passes through 

 membranes, is also particularly liable to escape both by the 

 skin and the kidneys, and is found in all the secretions; it 

 requires therefore to be supplied in quantity greater than 

 that in which it exists in the requisite amount of solid 

 aliment. The results of experiment, as well as general 

 experience, show that the addition of this substance to the 

 food is advantageous to nutrition ; and it is well known to 

 farmers that it is relished by cattle, and improves their con- 

 dition. Other mineral matters useful in the economy, as, 

 for example, salts of lime, occur in solution in the water 

 which we drink, as well as in our solid food. 



The organic matters used as food, like those which are met 

 with in the composition of the body, are divisible into nitro- 

 genous and carbonaceous. Nitrogenous foods are of two 

 kinds, namely, albuminoid or proteid substances, and gela- 

 tinoids. Albuminoids are obtainable from both vegetable 

 and animal sources, though much more abundantly from the 

 latter; in flesh diet they are supplied in the forms of muscle- 

 fibrin and albumen ; in eggs albumen is furnished, mingled 

 with oil in the yolk, and in the white altogether pure ; and 

 in milk the albuminoid constituent is casein, distinguished 

 from albumen by not coagulating when heated. - Under the 

 title of gelatinoids may be conveniently grouped a set of 

 substances obtained from animal sources, and including not 

 only gelatin and chondrin, but the tissues which yield them. 

 Also, nearly allied to those substances in nutritive value 

 are kreatin and other flavouring ingredients in the juice of 

 meat. 



Carbonaceous foods are likewise of two principal 



