THE FOOD AND DIGESTION 323 



the outer layer of the flesh, leave all the constituents in only 

 slightly altered proportions. 



On the other hand, if a piece of flesh be put into cold 

 water and boiled, the proteids, the salts, and the various 

 extractive bodies which give it its flavour are extracted, and, 

 as the water warms, the fats also are dissolved out, and the 

 meat becomes poorer in these constituents, while the sur- 

 rounding water becomes a soup. In this soup the dissolved 

 proteids precipitate as the temperature rises, and when the 

 soup is cooled they rise to the top with the fats, and are 

 generally removed as a scum. Hence soups are poor in the 

 proximate principles of food, but rich in the extractives and 

 salts of meat. 



If, however, the piece of meat to be cooked is plunged into 

 a large quantity of boiling water, the proteids at its outer 

 part at once coagulate and form a covering which prevents 

 the loss of the nutrient material which occurs when the meat 

 is slowly boiled. 



Stewing is a modification of boiling by which much of the 

 nutrient material of meat is extracted, but this is served as a 

 gravy. 



It is in vegetables, however, that cooking is of the greatest 

 importance, since by it the cellulose envelopes which enclose 

 the digestible portions of the plant are ruptured. 



