MINERAL SUBSTANCES IN OUR DIETARY 121 



containing different amino-acids, one may thrive, while the other 

 wastes away and dies. For example, gelatin is a very poor type 

 of protein, because it does not contain the necessary amino-acids 

 for tissue building or tissue repair. On the other hand, the pro- 

 teins of milk contain the amino-acids necessary for growth. It is 

 estimated that there are about twenty of these amino-acids, and 

 that all of those essential for growth are found in milk, eggs, wheat 

 and a few other grains, and nuts. So it happens that most of us, 

 without knowing why, have used for food the proteins containing 

 the essential amino-acids. 



The Value of Mineral Substances in our Dietary. — It has long 

 been known that water and the various mineral salts it contains 

 are essential to life. The human body, by weight, is about two 

 thirds water. About 90 per cent of the blood is water. Water is 

 absolutely essential in passing off the waste of the body. When 

 we drink water, we take with it some of the inorganic salts used by 

 the body in the making of bone and in the formation of protoplasm. 

 Sodium chloride (table salt), an important part of the blood, is 

 taken in also as a flavoring upon our meats and vegetables. Phos- 

 phate of lime and potash are important factors in the formation of 

 bone. 



But it is only recently that scientists have learned how impor- 

 tant a part is played by minute quantities of certain mineral sub- 

 stances. For example, the clotting of our blood, without which 

 we should bleed to death from the smallest cut, appears to depend 

 on the presence of calcium in the blood. 



Some other salts, compounds of magnesium, potassium, and 

 phosphorus, aid the body in many of its most important functions. 

 The beating of the heart, the contraction of muscles, and the 

 ability of the nerves to do their work appear to depend on the pres- 

 ence of minute quantities of these salts in the body. Thus they 

 act as regulators of bodily activity. 



Vitamins and their Uses. — Far more wonderful regulating sub- 

 stances are the vitamins. While little is known of their chemical 

 composition, a good deal has recently been learned of what they 

 do, or, rather, of what their absence will cause. These mysterious 

 health-regulating substances are known as Vitamins A, B, C ; also 

 the recently-discovered Vitamins D and E. A glance at the table 



