ELEVENTH ANNUAL YEAR BOOK— PART XI 613 



into consideration, and as a matter of fact they always form the greater 

 part of the bulk of human food; hut of the animal foods which are usually 

 combined with the vegetable foods, milk is one of the cheapest. 



CARIC OF MILK AXD ITS USE IN THE HOME. 



In spite of the fact that milk is recognized as a nutritious and a cheap 

 food, there seems to be a general tendency to think of it not as a possible 

 substitute for other more expensive foods, but rather as an addition to 

 the bill of fare. To illustrate, milk is frequently used as a beverage, 

 without the reduction of the amount of meat or other proteid foods 

 served. From the point of view of the need of the body this may be 

 considered extravagant and the serving of a glass of milk or of a bowl- 

 ful of soup or of such desserts as custards and baked milk, or the use 

 of generous quantities of milk or white sauce on vegetables offers an 

 opportunity to cut down the allowance of meats and eggs. 



THE COMPOSITION OF MILK. 



The tendency to think of milk as a beverage rather than as an im- 

 portant source of food comes partly, no doubt, from the fact that it is 

 a liquid rather than a solid and that most liquid foods, such as clear soup, 

 coffee, and tea, contain very little that feeds the body. It is natural there- 

 fore, to associate milk with these rather than with the really nourishing 

 food materials. In order to overcome this tendency it is well to study 

 the solid products of milk as they are obtained by various processes 

 familiar in the dairy and in the kitchen as well as in the laboratory. 

 Before doing this it may be helpful to get an idea of the classes into which 

 the solids contained in milk are divided. These are: (1) Proteids, (2) 

 fats, (3) sugar, and (4) mineral matter. The fat and sugar serve as fuel 

 and the mineral matter is chiefly valuable for the making of bones and 

 teeth and other physiological purposes. The proteids serve as fuel like 

 the fats and sugar, but they are used also to make and to repair the mus- 

 cular tissues of the body. This double usefulness indicates why proteids 

 are so often referred to as the most important part of milk. 



Fat constitutes about 4 per cent of the weight of milk. All are famil- 

 iar with the common process of butter making by which the greater 

 part of the fat is separated from the other ingredients. The liquid which 

 remains and which is called buttermilk contains the rest of the nutrients 

 of the milk except the small portions which cling to the fat. On examin- 

 ing 'buttermilk after it has become a little sour, it may be seen that it 

 contains a white solid which in the process of churning has been divided 

 into very small particles. This solid is casein, the chief proteid of the 

 milk. It constitutes 3.3 per cent, or about one-thirtieth of the weight of 

 the milk. 



The familiar process of the souring of the milk also helps to an under- 

 standing of its corryiosition. When this takes place the casein and most 

 of the fat separate from the whey and form what is known as the curd. 

 When, however, the attempt is made to separate the curd completely 

 for the purpose of making cottage cheese, much of the fat is usually 

 carried off with the whey. This is particularly true if the curd is 



