24 



1916 ANNUAL REPORT 



necessary to consider the content of protein, fat and carbohydrate, apd 

 the caloric value, no special attention being paid to the mineral matter 

 or to the value of the individual proteins and fats. This is emphasized 

 by reference to the literature bearing on dietary studies and digestion 

 experiments. As has been previously stated, the general subject of the 

 mineral matter has only recently been accorded the prominence which it 

 demands, as evidenced by the fact that the first complete and comprehen- 

 sive bulletin by the Agricultural Experiment Stations of the United States 

 on the importance of the mineral elements in nutrition, was issued by Dr. 

 Forbes of the Ohio Station about seven years ago. 



It was formerly considered that the amount of mineral matter in any 

 diet or ration, particularly for the adult animal, was ample and that no 

 further attention need be paid to this matter, owing to which, as above 

 mentioned, in the compounding of rations and diets only the organic 

 nutriments were considered. The older views have been gradually changed 

 to meet the results of late nutrition investigations, particularly with ref- 

 erence to not only the amount but the nature of the minerals ingested 

 by animals, and this is particularly true in connection with human die- 

 taries. 



The mere statement that a combination of foods contains so many 

 grams of mineral matter or such and such a percentage of mineral 

 matter is almost meaningless as far as its physiological value is con- 

 cerned. Not only must there be an adequate supply of mineral matter 

 but there must be an adequate supply of each of the chemical elements 

 necessary and furthermore these must bear some quantitive relation to each 

 other, otherwise the diet is unbalanced in this respect. 



The most important elements which we have to consider are iron, 

 calcium, magnesium, potassium, sodium, chlorin, sulphur, and phosphorus, 

 and it may be said that these elements, which are most important as 

 far as animal nutrition is concerned, are equally important to the soil 

 as plant food. 



The question may well be asked if these mineral elements are so 

 important, why were not earlier investigations conducted with reference 

 to them. As Dr. Forbes writes: 



''There are a number of reasons why our knowledge of the func- 

 tions of the mineral elements in nutrition has not kept pace with our 

 advancing knowledge along other lines. First, animals need compara- 

 tively little of the mineral nutrients in their food; second, animals' 

 bodies contain considerable reserve supplies of the mineral nutrients 

 which can be drawn upon in case of need, so that a deficiency of the food 

 in certain mineral nutrients is not at once made apparent by the be- 

 haviour of the animal; third, the excretion into the intestine of waste 

 products containing mineral elements, and their consequent appearance 

 in the feces along with undigested mineral nutrients prevents an ac- 

 curate judgment as to the digestibility of the same; fourth, the rediges- 

 tion and reassimilation of mineral matter from certain waste products 

 which have been excreted into the intestine, thus resulting in a repeated 

 utilization of the same nutrient substance, tends to obscure the facts 

 regarding the nutrient in question; and fifth, most foods, though by 



