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 which 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 monosaccharide. 

 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 : 



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

 proteid, nucleoproteid, etc.; gelatin, elastin, etc. These furnish nitrogen in 

 available form. 



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



Fats. Such as olein. 



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 proteids 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 repre- 

 sentatives 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 i8 per cent, veal 16.5, and pork 10. 

 Beef is firmer, more satisfying, and is supposed to be more strengthening than 



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