434 THE HUMAN BODY 



which will not melt in the intestines and so passes on unabsorbed; 

 although from its composition it would be useful as a food could it 

 be digested. A distinction is sometimes made between fats proper 

 (the adipose tissue of animals consisting of fatty compounds in- 

 closed in albuminous cell-walls) and oils, or fatty bodies which are 

 not so organized. 



Proteins occur as the chief constituent of animal foods, lean 

 meat for example being 90 per cent protein after its large water 

 content is removed. Eggs and milk contain considerable amounts 

 of protein also. Proteins occur to a greater or lesser degree in 

 most vegetable foods. The gluten of wheat is protein; beans and 

 peas contain a larger percentage of protein than any other food 

 except cheese. 



The albuminoid of connective tissue, which is present in all 

 meat, is by cooking converted into gelatin, a digestible protein. 



Mixed Foods. These, as already pointed out, include nearly all 

 common articles of diet; they contain more than one nutrient. 

 Among them we find great differences; some being rich in pro- 

 teins, others in starch, others in fats, and so on. The formation 

 of a scientific dietary depends on a knowledge of these charac- 

 teristics. The foods eaten by man are, however, so varied that we 

 cannot do more than consider the most important. 



Flesh. This, whether derived from bird, beast, or fish, consists 

 essentially of the same things muscular fibers, connective tissue 

 and tendons, fats, blood-vessels, and nerves. It contains several 

 proteins, especially myosin and myogen; gelatin-yielding matters 

 in the white fibrous tissue; stearin, palmatin, and olein as repre- 

 sentatives of the fats; and a small amount of carbohydrates in the 

 form of glycogen and grape-sugar, or some chemically allied sub- 

 stances. Flesh also contains much water and a considerable 

 number of salines, the most important and abundant being po- 

 tassium phosphate. The nitrogenous extractives (Chap. I) give 

 much of its taste to flesh; and small quantities of various of these 

 substances exist in different kinds of meat. There is also more 

 or less yellow elastic tissue in flesh; it is indigestible and useless 

 as food. 



When meat is cooked its white fibrous tissue is turned into 

 gelatin, and the whole mass becomes thus softer and more easily 

 disintegrated by the teeth. When boiled some of the protein 



