66 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



and sugars. They are of definite chemical composition con- 

 taining carbon, hydrogen and oxygen, but no nitrogen. The 

 hydrogen and oxygen which they contain are always in the 

 proportion to form water, i. e., two atoms of hydrogen to one 

 of oxygen. The starches are found chiefly in wheat, corn, 

 oats and other grains ; also in potatoes, peas, beans and in the 

 roots and stems of many plants, and in some fruits. Starch 

 is found in a pure state, as a white powder, in arrowroot and 

 corn-starch. The sugars are of several kinds, the principal 

 being : cane sugar, beet sugar, maple sugar, grape sugar which 

 is found in grapes, peaches and other fruits, and malt sugar 

 which is obtained from malt. These are all obtained from 

 vegetable tissue, however a few are found in or formed by 

 the animal organisms, as glycogen, dextrose and lactose. 

 They are the cheapest foods from financial and digestive 

 standpoints and constitute the main bulk of articles eaten. 

 They contain more oxygen than do the fats, and are more 

 easily oxidized and converted into heat and muscular energy. 

 In fact, their great physiological value lies in the ease with 

 which they are burned up in the body. They furnish the 

 main part of the fuel necessary to the running of the animal 

 mechanism. They may also be converted into fatty tissue by 

 the body. 



IV. The fats are ingested with both animal and vegetable 

 diets. They are compounds of carbon, hydrogen and oxy- 

 gen. The principal fats are stearin, palmatin, margarin and 

 olein. These exist in varying proportions in the fat of ani- 

 mals, in the various vegetable oils and in milk, butter, lard 

 and in other foods and vegetable substances. The fats contain 

 no nitrogen, and, Jike carbohydrates, their great physiological 

 value lies in the fact that they are destroyed in the organism 

 to produce energy, whether in the form of heat or muscu- 

 lar exercise. They are handled and converted less readily by 

 the system than the carbohydrates, and consequently tax the 

 digestive powers more. But it is found that, weight for 

 weight, they are the more efficient in the production of 



