354 BIOLOGY FOR BEGINNERS 



work for which they have become adapted, and without which they 

 will not remain in health. 



Cooking. Man is the only animal which has learned to build a 

 fire, hence is the only animal to use cooked food. This is not an 

 unmixed blessing, for our digestive apparatus and especially our 

 teeth are inherited from our animal ancestors, and, when provided 

 with cooked food, are relieved of work for which they were adapted. 

 This leads to disuse and so to degeneration. One seldom hears of 

 the lower animals suffering from decayed teeth or indigestion, 

 both of which are almost universal in man, due partly to too abund- 

 ant, too delicately prepared, and unnatural foods. 



Cooking of food performs three functions: First, it changes the 

 mechanical and chemical condition so as to make it more easily 

 digestible ; second, it makes food more appetizing in appearance or 

 flavor, which quickens the flow of digestive fluids and actually aids 

 digestion; third, the high temperature kills any dangerous bac- 

 teria, organisms, or parasites that the food may contain. This is 

 very important. 



Cooking meat develops its pleasing taste and odor, softens con- 

 nective tissue, and makes it " tender," though too high temperature 

 may harden the proteids of the lean portions. Beef extracts and 

 thin soups are very agreeable to the taste, but contain very little 

 nourishment since the meat proteids and fats are not soluble in 

 water. These broths are useful as appetizers or mild stimulants 

 but are of slight value as food. 



In cooking eggs, especially by frying, the proteid (albumen) is 

 hardened and made less digestible than in the raw state. Milk, 

 also, if heated to boiling, is made less valuable as food; though 

 when pasteurized the heat is regulated so as to kill most bacteria, 

 but not to reach a point high enough to impair its food value. 

 When the vegetable foods are cooked the changes are chiefly the 

 softening of the cellulose and the breaking of the insoluble walls 

 around the starch grains, thus exposing them to digestive fluids 

 and partly dissolving the starch in the hot water or steam. 



In baking all flour foods, the aim is to make the material " light," 

 and porous so as to be more easily broken up and digested in the 



