140 THE STORY OF MILK 



are not equal in this respect. Pound for pound, when 

 burned in the body, the fats yield 234 times as much 

 heat as protein or the carbohydrates. 



Mineral Matters. — Finally there are in all foods the 

 mineral matters, a group containing a number of salts 

 which are indispensible because they are constituents 

 of every part of the body. Phosphate of lime, for in- 

 stance, makes up one-half of the substance of the bones, 

 and the sulphates and chlorides of potash and soda, 

 iron, etc., are everywhere present in smaller quantities. 

 No food in which any of them is lacking is complete. 



Relation. — The value of a food depends largely upon 

 the relation of one group of nutrients to another. 

 Proper nutrition can only be obtained when a sufficient 

 amount of flesh-forming as well as of heat-producing 

 nutrients are present, when the ''nutritive ratio" is 

 properly balanced for the particular purpose in view, 

 be it the growth of the child, the maintenance of the 

 body, the restoration of matter consumed by labor of 

 body or brain, or the supply of heat to make up for 

 cold surroundings. 



Milk contains all of these groups of nutrients. The 

 protein is represented in milk by the casein and al- 

 bumin, the fats by the butter-fat, the carbohydrates 

 by milk-sugar, and the mineral matters by the milk- 

 ash. Human milk contains them in a perfect propor- 

 tion for infants, and for all purposes of nutrition cow's 

 milk may be used to make up a ''balanced ration," 

 if not alone, then in connection with other food. 



Nutritive Ratio. — As we said before, the "nutritive 

 ratio" of a food means the ratio of its flesh-forming 

 constituents — proteins — to its heat-producing nutri- 

 ents — carbohydrates and fats. Cow's milk, containing 



