66 THE PHYSIOLOGY OF DIGESTION AND ABSORPTION 



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 organism, as glycogen, dextrose and 

 lactose. They are the cheapest foods from financial and digest- 

 ive 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 oxygen. 

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

 These exist in varying proportions in the fat of animals, in the 

 various vegetable oils and in milk, butter, lard and in other foods 

 and vegetable substances. The fats contain no nitrogen, and, like 

 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 muscular 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 more efficient in the production 

 of energy than are the carbohydrates. They also furnish fuel 

 for the running of the body mechanism. 



V. The proteids form a large part of all living organisms and 

 are absolutely necessary to animal life. They are very stable 

 compounds and are found in both animal and vegetable foods. 



