210 HANDBOOK OF PHYSIOLOGY. 



To supply the loss of nitrogen and carbon, it is found by experience 

 that it is necessary to combine substances which contain a large amount 

 of nitrogen with others in which carbon is in considerable amount ; and 

 although, without doubt, if it were possible to relish and digest one or 

 other of the above-mentioned proteids when combined with a due quan- 

 tity of an amyloid to supply the carbon, such a diet, together with salt 

 and water, ought to support life ; yet we find that for the purposes of 

 ordinary life this system does not answer, and instead of confining our 

 nitrogenous foods to one variety of substance we obtain it in a large 

 number of allied substances, for example, in flesh, of bird, beast, or fish; 

 in eggs ; in milk ; and in vegetables. And, again, we are not content 

 with one kind of material to supply the carbon necessary for maintaining 

 life, but seek more, in bread, in fats, in vegetables, in fruits. Again, 

 the fluid diet is seldom supplied in the form of pure water, but in beer, 

 in wines, in tea and coffee, as well as in fruits and succulent vegetables. 



Man requires that his food should be cooked. Very few organic sub- 

 stances can be properly digested without previous exposure to heat and 

 to other manipulations which constitute the process of cooking. 



A. Foods containing nitrogenous principles chiefly. 



I. Flesh of Animals, of the ox (beef, veal), sheep (mutton, lamb), 

 pig (pork, bacon, ham). 



Of these, beef is richest in nitrogenous matters, containing about 20 

 per cent, whereas mutton contains about 18 per cent, veal, 16.5, and 

 pork, 10 ; the flesh is also firmer, more satisfying, and is supposed to be 

 more strengthening than mutton, whereas the latter is more digestible. 

 The flesh of young animals, such as lamb and veal, is less digestible and 

 less nutritious. Pork is comparatively indigestible and contains a large 

 amount of fat. 



Flesh contains : (1) Nitrogenous bodies : myosin, serum-albumin, 

 gelatin (from the interstitial fibrous connective tissue); elastin (from the 

 elastic tissue), as well as hcemoglobin. (2) Fatty matters, including 

 lecithin and cholesterin. (3) Extractive matters, some of which are 

 agreeable to the palate, e.g., osmazome, and others, which are weakly 

 stimulating, e.g., Jcreatin. Besides, there are sarcolactic and inositic 

 acids, taurin, xanthin, and others. (4) Salts, chiefly of potassium, cal- 

 cium, and magnesium. (5) Water, the amount of which varies from 15 

 per cent in dried bacon to 39 in pork, 51 to 53 in fat beef and mutton, 

 to 72 per cent in lean beef and mutton. (6) A certain amount of carbo- 

 hydrate material is found in the flesh of some animals, in the form of 

 inosite, dextrin, grape sugar, and (in young animals) glycogen. 



