CHAPTER VIII 

 FOOD AND DIGESTION 



THE term digestion includes those changes taking place in the body which 

 bring the materials of the food into such condition that they may be taken up 

 by the blood and lymphatic vessels and thus rendered available for the metab- 

 olism of the tissues. In the process the foods are rendered more soluble 

 and more diffusible. Certain bodies which are already soluble and diffusible 

 are converted into forms w r hich are more available for the tissues; as an ex- 

 ample, cane-sugar, although both soluble and diffusible, cannot be readily 

 used by the body until it is converted from a disaccharide to a monosaccha- 

 ride. In fact, few of the food materials are fit for immediate use when taken 

 into the body and are therefore practically useless until digested. 



FOOD AND FOOD PRINCIPLES. 



We have been accustomed to classify foods into certain main groups, 

 chiefly according to their chemical character, as follows: 



Proteins. Such as albumin, myosin, gluten, casein, etc.; gluco- protein, 

 nucleoprotein, etc.; gelatin, elastin, etc. These furnish nitrogen in avail- 

 able form. 



Carbohydrates. Such as starch, dextrose, cane-sugar, etc. 



Fats. Such as tristearin, tripalmitin, triolein. 



Minerals. The various salines found in animal and vegetable food. 



Water. 



The classes of foods just enumerated usually exist in mixtures rather than 

 in simple forms, as, for example, a beef roast contains a representative of each 

 of the five classes enumerated, though it is composed chiefly of water, pro- 

 teins, and fats. The human body is capable of using materials of a great 

 variety of forms, but most of these have the foods mixed in such a way as to give 

 representatives of each of the classes above in certain general proportions. 



Nitrogenous Foods. The Flesh of Animals, e.g., beef, veal, mutton, 

 pork, bacon, ham, chicken, eggs, milk, etc., are typical nitrogenous foods. 



Of these, beef and eggs are richest in nitrogenous matters, containing 

 about 20 per cent. Mutton contains about 18 per cent., veal 16.5, and pork 

 10. Beef is firmer, more satisfying, and is supposed to be more strengthen- 

 ing 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 

 contains a large amount of fat and is, therefore, comparatively indigestible. 



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