The last and least understood of the groups of food substances is mineral substance or ash. Now, the chemist determines mineral substance by burning the food and analyzing the residue. In the intense heat numerous chemical changes take place and the substances that come out of the furnace are entirely different from those contained in the fresh food. The lay reader will probably ask why the chemist does not analyze the substances of the fresh material. The answer is that he doesn't know how. Progress is made every year but the whole subject is yet too much clouded in obscurity to be of any practical application. At present the feeding of mineral substance, like the feeding of protein, can best be learned by experimenting directly with the foods rather than by attempting to go by their chemical composition. In practice it is found that green feed supplies something which grain lacks, presumably mineral salts. Moreover we know that such food fed fresh is superior to the same substance dried. This may be because of chemical changes that occur in curing or simply because of greater palatability. The other chief source of mineral matter is meat preparations with or without ground bone. Recent experiments at Rhode Island have attempted to show the relative value of the mineral constituents of meat by adding bone ash to vegetable proteids, as linseed and gluten meal. The results clearly indicate that mineral matter of animal origin greatly improves the value of the vegetable diet, but that the latter is still sadly deficient. Of course the burning process used in preparing the bone ash may have destroyed some of the valuable qualities of the mineral salts. Practically, we do not care whether the value of animal meal be due to protein, mineral salts or both. In time the world will become so thickly populated that we cannot afford to rear cattle and condemn a portion of the carcass to go through another life cycle before human consumption. By that time the necessary food salts will doubtless be known and we will be able to medicate our corn and alfalfa and do away with the beef scrap. The poultrymen will do well, however, not to count on the chemistry of the future, for the chemist that makes the "tissue salts" for the hen may manufacture human food with Niagara power and fresh eggs will come in tin cans. How the Hen Unbalances Balanced Rations.