432 FORBES! MINERAL ELEMENTS IN NUTRITION 



soil fertility, heat, light, and moisture, which affect their mineral 

 content affect the food value of these products for animals. 

 Similarly all of those processes of treatment of foods, as to con- 

 ditions of harvesting, storage, manufacture, preservation, and 

 preparation which affect their mineral content have a bearing 

 on the nutrition of animals. Further, the almost unlimited 

 freedom of choice of foods afforded by our markets and our 

 prosperity, a freedom which may profoundly affect the mineral 

 content of the diet, furnishes a basis of interest and an obli- 

 gation to understand. Finally, the mineral requirements of 

 men and animals in their various conditions and stages of life, 

 growth, health, and activity differ greatly in such ways as to 

 demand our attention, since the whole range of success and profit 

 in practical animal nutrition lies close, and ever closer, to maxi- 

 mum possibilities. 



As this subject relates to stock feeding, we find that modern 

 tendencies give it a special importance that it had not in times 

 past. The forced feeding of our early-maturing meat animals 

 and the selective improvement of our poultry and our dairy 

 cows for greater productive capacity call for a higher percentage 

 of mineral nutrients in foodstuffs than was necessary in the old 

 days of less intense production. The requirement of mineral 

 nutrients for mere maintenance is slight in amount, compared 

 with the requirement for the production of flesh, eggs, and milk; 

 hence, the more efficient the producer, the higher must be the 

 ash content of the food. 



My own investigations in this field consist of studies of the 

 chemistry of foods, and metabolism experiments with swine 

 and milch cows. I shall review briefly some of the conclusions 

 from this program of work. 



Our studies on foods comprise a series of complete ash analyses, 

 with computations of the elements to normal solutions, these 

 data being considered in relation to the balance of base and acid 

 in the organism; also a study of the mineral nutrients of blue- 

 grass, and factors which affect the quantities present; and a 

 study of the iodine content of foods in relation to the prevalence 

 of goiter. 



