Page:Popular Science Monthly Volume 22.djvu/404

390 grain, consumed from twenty-six to thirty pounds of dry substance per week, for each hundred pounds of live weight, and yielded one pound of increase in weight for each four or five pounds of dry substance in their food. Oxen, therefore, consume more dry substance of food, in proportion to their weight, than sheep, and sheep consume more than pigs, while, in return for feed consumed, pigs yield more than sheep, and sheep gave better results than oxen. It must be remembered in this connection, as has already been pointed out, that the food of oxen contained more woody fiber, while that of the pigs was comparatively concentrated and digestible, and therefore of better quality. With sheep of different breeds it was found that, under the same conditions as to age and fatness, the food consumed was in proportion to their live weight. The relative value of the larger and smaller breeds seems, therefore, to depend, to a great extent at least, upon their habits and hardiness, and their adaptation to the conditions of the locality in which they are placed.

In studying these experiments, it will be well to keep in mind the twofold function of food in the animal economy: first, as the source of energy for the performance of work in the various organs of the body, which is required in elaborating the peculiar animal products sought in the process of feeding (as milk, flesh, wool, etc.), and in carrying on the processes of repair and reconstruction to maintain the integrity of the animal machinery; and, in the second place, as supplying the materials for the construction or elaboration of the special animal products. The popular notions of nutrition assume that this supply of materials in the food for the new product sought is the most important, and the supply of energy for the performance of work is overlooked or assigned a subordinate position.

The results of the experiments relating to the use and ultimate disposition of the food consumed by animals when fattened under average conditions, as to feed and increase, are given in the following table:

The figures in the last column of the table are not intended to represent all of the internal work of the system. They simply show the amount of non-nitrogenous constituents that are not accounted for in the stored-up increase, or in the manure, and thus are properly designated as having been used in internal work. From an agricultural stand-point, the proportions of food-constituents stored up as increase,