MILK AS A FOOD 141 



3.25% protein, 4% fat and 5% milk-sugar, has a nu- 

 tritive ratio of 1:4.3, i. e., 1 part of protein to 4.3 parts 

 of heat-giving nutrients, counting the fat equal to 234 

 of carbohydrates (multiplying the 4% fat by 234 makes 

 9, added to the 5% of sugar, makes 14; 3.25 to 14 

 equals 1 to 4.3). Skim milk, containing 3.4% protein, 

 0.2% fat, and 5.1% sugar, has a ratio of 1:1.6 (3.4: 

 5.45). Mother's milk, containing 2% protein, 4% fat, 

 and 6.5% carbohydrates, has a ratio of 1:7.75. To 

 substitute cow's milk for mother's, it must therefore 

 be ^^ modified." 



Calories. — Another way of comparing various foods 

 than by the nutritive ratio is by measuring their ''fuel 

 value" or energy-producing capacity. The amount of 

 heat required to raise the temperature of one kilogram 

 of water 1° C, or one pound 4° F., is called a calorie. 

 By extensive feeding experiments the caloric value of 

 the various nutrient groups has been estimated as 

 follows : 



Protein at 1820 calories per pound * 

 Fats '' 4040 " " 



Carbohydrates at 1820 calories per pound 



Measured by this rule the fuel value of: 



Whole milk is 310 calories per pound 



Skim milk '' 160 " " " 



Full cream cheese is 1885 '' '' " 

 Butter is 3410 " " " 



Compared with other food, milk, although not suited 

 to act as the sole food of adults, is one of the best and 



* W. O. Atwater, Farmers' Bulletin No. 142. 



