It has been observed that successive cultivation exhausts the soil, and deprives it of the constituents necessary for vegetable development. If so, it follows that there will be a deficiency of silecia, carbonate of lime,--in short, a loss of carbon, hydrogen, nitrogen, and oxygen, not of phosphate of lime alone. The fields might be made to produce the requisite amount of nutriment by replacing every year, in the form of animal excrement, straw, wood-ashes, and charcoal, as much as we remove from them in the form of produce. An increase of crop can only be obtained when we add more to the soil than we take away from it. "In Flanders, the yearly loss of the necessary matters in the soil is completely restored by covering the fields with ashes of wood or bones, which may, or may not, have been lixiviated. The great importance of manuring with ashes has been long recognized by agriculturists as the result of experience. So great a value, indeed, is attached to this material in the vicinity of Marburg, and in the Wetterau,--two well-known agricultural districts,--that it is transported, as a manure, from the distance of eighteen or twenty-four miles. Its use will be at once perceived, when it is considered that the ashes, after being washed with water, contain silicate of potass exactly in the same proportion as in the straw, and that their only other constituents are salts of phosphoric acid." It is well known that phosphate of lime, potass, silecia, carbonate of lime, magnesia, and soda are discharged in the excrement and urine of the cow; and this happens when they are not adapted to assimilation as well as when present in excess. If it is clearly proved that the bones of a cow are weak, then we should be inclined to prescribe phosphates; if they are brittle, we should prescribe gelatinous preparations; but not in the form of bone dust: we should use linseed, which is known to be rich in phosphates. At the same time, the general health must be improved. It is well known that some cows cannot be fattened, although they have an abundance of the best kind of fodder. In such cases, we find the digestive organs deranged, which disturbs the equilibrium of the whole animal economy. The food may then be said to be a direct cause of disease.