and voided as manure, are of the first importance, as these are the two factors that determine the economy of feeding. The expenditure of energy in the system, from the nitrogenous constituents of the food, is not, therefore, included in the last column, as all of the nitrogen of the food that is not stored up as increase is finally excreted in the urine. The first and second columns of the table, therefore, include the nitrogenous and the mineral substances of the food, and any energy that may have been expended as a result of their metamorphoses is not represented in the table.
From the data presented, it appears that more than one half (57*3 per cent) of the food of oxen when fattening is required in internal work, or in keeping the animal machinery in repair, to say nothing of the energy expended by the nitrogenous constituents, while but 6·2 per cent is stored up as increase in weight, and more than one third is found in the manure. With sheep, 8·0 per cent of the food is stored up as increase, less than one third appears in the manure, and 60·1 per cent is used in work of the system. The pigs give 17·6 per cent of the food in increase, or more than twice as much as the sheep, while nearly two thirds is required for internal work, and the manure contains less than one half as much as in the case of the oxen. The pigs store up a much larger proportion of their food as increase than either the sheep or the oxen, but a larger percentage is used in internal work, and less appears in the manure. The increased expenditure in work would naturally follow from the larger amount stored up as increase, which involves as a matter of course an expenditure of energy in its elaboration. But this is not the whole truth, as will be seen on making a comparison of the figures in the first and last columns of the table. For a given amount of increase stored up, the oxen actually expend more in internal work than sheep, and the sheep expend more than the pigs It evidently costs more, in internal work of the system, to elaborate the stored-up increase from the crude feed of the oxen than from the more nutritive food of the pigs. When the facts are examined from a different stand-point, the relations of the increase to work of the system will be more clearly seen, as in the following table, which gives the results obtained from a given live weight of the animals in a given time:
|ANIMALS||For each 100 pounds of live weight, per week.|
|Stored as increase.||Dry substance.|
|Consumed in food.||Recovered in manure.||Used in internal work of the system, and not accounted for in manure and increase.||Used in internal work for each one pound of stored increase.|