Page:Popular Science Monthly Volume 22.djvu/401

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slaughtered at once, and its contents of nitrogenous substance, fat, mineral matter, etc., accurately determined. The other was fed on a mixture consisting of bean-meal, lentil-meal, and bran, each one part, and barley-meal three parts, given ad libitum, but accurately weighed, for a period of ten weeks, when it had nearly doubled its weight. The animal was then slaughtered, and analyzed as the other had been. The composition of the food was also determined by analysis."

According to the generally accepted theory of nutrition at the time the Rothamsted feeding experiments were planned, the constituents of foods were divided into two leading groups, each of which was assumed to serve a special purpose in the system. It was believed that the nitrogenous constituents were the only nutritive elements, and that the carbonaceous constituents (including the fat, starch, etc.) served as fuel, which was burned in the system to keep up the animal heat. In the published analyses of animals and of foods at Rothamsted, this distinction was recognized, and the results are given in terms of these groups of constituents. A summary of the results of the analyses of the ten animals described above is given in the following table, in percentage values of groups of constituents, in the carcass and in the total offal parts:

PSM V22 D401 Animal nutrition contents.png

This table furnishes some important data for an intelligible discussion of the economics of nutrition, with reference to human dietaries, but there are many points of interest presented in the details of the analyses of these animals that can not be embraced in such a tabular abstract. In the carcass of the fat calf, it will be noticed, the percentage of nitrogenous substance and of fat is the same, while in the other animals the fat is largely in excess, even in those in store condition. There is likewise a larger percentage of nitrogenous substance in the offal parts than in the carcass in all cases. It was also found that "the fat of the bones bears but a small proportion to that of the whole carcass, while, of the whole of the nitrogen of the carcasses, perhaps not less than one fifth will be in the bones. . . . As the animal