214 HAND-BOOK 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 quantity 

 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. Arid, again, we are not content with one kind of ma- 

 terial 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 cof- 

 fee, 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. It will 

 be well, therefore, to consider the composition of the various substances 

 employed as food, and then to consider how they are affected by cooking. 



I 



A. FOODS CONTAINING PRINCIPALLY NITROGENOUS BODIES. 



I. Flesh of Animals, especially 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, gela- 

 tin (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., 

 kreatin. Besides, there are sarcolactic and inositic acids, taurin, xanthin, 

 and others. (4) Salts, chiefly of potassium, calcium, 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 young animals, in the form of inosite, dextrin, grape 

 sugar, and (in young animals) glycogen. 





