VITAMINS 267 



call the per diem nutrient needs of the human machine. 



Aside from the organic nutrients present in a food, 

 however, it has been found that the body also requires 

 certain mineral salts. The manufacture of bone, for 

 example, is a matter of lime deposition and we are learn- 

 ing that to deposit this lime as bone the body requires, 

 not only lime salts, but a certain amount of phosphorus. 

 Again the prevention of various bad conditions lumped 

 collectively under the name of acidosis requires that our 

 blood be kept nearly neutral in reaction and the carbo- 

 nates and phosphates play an important part in this regu- 

 lation. Mineral salts, then, constitute a fourth nutrient. 



We are accustomed, then, to say that the second 

 principle for guidance in food selection is to make sure 

 that the foodstuffs contain the proper kinds and 

 amounts of nutrients, including under this term car- 

 bohydrates, fats, proteins, and mineral salts. 



The next discovery was the demonstration that pro- 

 teins differ in nutritive value and that not only must 

 the body have its fifty grams of protein per day, but it 

 is extremely fussy as to the kind of protein it demands. 

 As a result of the studies of many chemists working in 

 this field we know that proteins are to be thought of as 

 mosaics made up of separate chemical pieces and that 

 there are some eighteen of these pieces, nearly all of 

 which are absolutely necessary to make a body- 

 satisfying protein. These pieces are known chemically 

 as amino acids, but the principle involved is covered if 

 we say that not only must we be sure of the amount of 

 protein, but we must also assure ourselves as to its 

 quality or make-up. 



