MINERAL MATTERS, WATER, ETC. 



419 



ship has not yet been determined, though some recent experiments seem to 

 be pertinent, page 431. 



Mineral Matters, Water, etc. The chief mineral constituents of 

 the foods are sodium, potassium, calcium, magnesium, and iron, together 

 with chlorine, sulphur, and phosphorus. The inorganic substances are not 

 a source of heat. They may supply a certain amount of energy, as osmotic 

 energy, but this is of no significance as compared with their influence on the 

 metabolism of organic substances. An animal fed on a normal food deprived 

 of the mineral constituents survives only a few weeks at most. 



The amount of mineral matter in the tissues of the human body, exclusive 

 of the skeletal parts, is about one per cent. It is safe to say that this is chiefly 

 in complex organic combination in the body. The daily quantity excreted 

 is about twenty to thirty grains. This quantity enters the body in the food, 

 chiefly in combination with complex compounds. It is a question as to what 

 per cent of inorganic salts, like the calcium, the phosphates, and the iron, 

 is available when taken into the body in inorganic form. 



We have discussed in previous chapters the role of certain salts in 

 their influence on metabolism; for example, of sodium, potassium, calcium, 

 iron, etc. Foods like milk and eggs are especially rich in calcium and 

 phosphorus, and are particularly desirable for young children, the for- 

 mer for its influence on the growth of the skeleton, the latter for the same 

 reason and as a stimulator of growth of protoplasm in general. Lack of 

 mineral constituents, especially calcium compounds, in food shows its in- 

 fluence on metabolism in the disease known as rickets. 



Investigations are in progress at the present time which may demonstrate 

 more fully the specific influence of phosphorus on animal nutrition and on 

 growth. Tunnicliff has just demonstrated that an increase of the phos- 



NUTRITION EXPERIMENT IN FIVE-MONTHS-OLD PIGS. (E. B. FORBES.) 



