62 THE CHEMISTRY OF FOOD. 



also contain starch ; and has the same chemical composi- 

 tion as the latter, but is much less nutritious. In the 

 East, gum-arabic and similar substances are largely em- 

 ployed as food. Persons who travel by caravan across vast, 

 sandy deserts, find such substances well adapted to their 

 wants, since they are not perishable, and are easily packed 

 and carried. 



28. Stimulating Substances. The three classes of 

 food-principles already considered the Albuminoids, the 

 Fats, and the Sugars comprise all the more important 

 organic ingredients of our food. There are, besides, a 

 great variety of coloring and flavoring matters that stim- 

 ulate or increase the appetite for food by appealing to the 

 eye and taste; but they are not nutritious, and are quickly 

 separated from the truly useful substances, and do not 

 long remain in the body. Among these may be classed 

 spices, flavors of fruits, tea, coffee, and vegetable acids. 



29. Necessity of a Regulated Diet. A great vari- 

 ety of experiments have been tried in order to test the rela- 

 tive value of the different nutritive principles. They have 

 been practised to some extent upon man, but chiefly upon 

 those inferior animals which require a similar diet to man. 



30. By this means it has been demonstrated that first, 

 when any one of these substances is eaten exclusively, the 

 body is imperfectly nourished, and life is shortened. Dogs 

 fed exclusively upon either albumen, fat, or sugar, soon die 

 of starvation. Second, a diet long deprived of either of 

 these principles, is a fertile cause of disease; for example, 

 on ship-board, where fresh vegetables are not dealt out for a 

 long period, scurvy becomes prevalent among the sailors. 

 They are, however, to a certain extent mutually convertible, 

 and thus the missing article is indirectly supplied. For 



28. The three classes of food principles ? What besides? What is ?aid of 

 them ? Name the articles not nutritions. 



29. What is said of experiments that have been tried ? 



30. What has been demonstrated in the first place? Example? Second de- 

 monstration ? Example ? Give the illustration in relation to convertibility. 



