CHAPTER IX. 



FOOD AND DIGESTION. 



THE object of digestion is to bring the materials of the food into 

 such a condition that they may be taken up by the blood and lymphatic 

 vessels, and so rendered available for the wants of the system. It makes 

 the foods soluble and diffusible, and also converts bodies already soluble 

 and diffusible into forms which can be utilized, e.g., cane sugar, al- 

 though soluble and diffusible, cannot be used by the body until it has 

 been split into two molecules of monosaccharide. Very few of these 

 materials are fit for this purpose when taken into- the body, and the 

 majority would therefore be to all intents and purposes quite useless 

 unless digested. 



It is unnecessary to mention all the various substances which may 

 have been used as food at some time or another, and we shall confine our 

 attention, therefore, to the chief and most familiar articles of diet. 



We find, then, that foods may be divided into classes corresponding 

 closely to those employed to describe the chief substances of which the 

 animal body consists. This classification may be recapitulated as fol- 

 lows : 



ORGANIC. 



I. Foods primarily containing Nitrogenous substances, consisting of Pro- 

 teids, e. g., albumen, casein, myosin, gluten, legumin and their allies; 

 and Albuminoids, e.g., gelatin, elastin, and chondrin. 



II. Food primarily containing Non-Nitrogenous substances, comprising : 

 (1.) Amyloid or saccharine bodies, chemically known as carbo-hydrates ; 



e.g. , starches and sugars. 



(2.) Oils and fats. These substances contain carbon, hydrogen, and oxy- 

 gen, but the oxygen is less in amount than in the amyloids and 

 saccharine bodies. 



INORGANIC. 



I. Foods which supply Mineral and saline matter. 

 II. Liquid food containing chiefly Water. 



Man requires that the chief part of his food should be cooked. Very 

 few organic substances can be properly digested without previous ex- 

 posure to heat and to other manipulations which constitute the process 

 of cooking. 



Organic nitrogenous foods. 



The Flesh of Animals, e.g., 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 



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