Page:Popular Science Monthly Volume 22.djvu/398

384 not only from the light thrown on many of the obscure processes of nutrition, but also in laying a foundation for a consistent system of feeding, in which the relations of the food consumed to the special animal products obtained, and to the value of the manure produced, as an incident of the process, are clearly traced.

In determining the amount of food and of its several constituents consumed for a given live weight of the animal in a given time, and the amount of food and of its several constituents required to produce a given amount of increase in live weight, several hundred animals, including oxen, sheep, and pigs, were subjected to experiment. In these researches, selected lots of animals were supplied, for weeks or months, with weighed quantities of food of known composition, as determined by analysis, and especially adapted to the particular point under investigation. The animals were weighed at the beginning, at intervals during the progress, and at the close of the experiment.

The composition of the manure produced from a given amount and quality of food consumed, by oxen, sheep, and pigs, was determined in a large number of cases by analyzing average samples of the food, and then making an analysis of the solid and liquid excretions of the animals. In these experiments, the oxen were fed in boxes in which the manure was preserved with litter of known composition. After feeding for from five to nine weeks, the total manure produced was carefully mixed, weighed, sampled, and analyzed. By this method the solid and the liquid excreta were not separately examined. With sheep no litter was used, the animals, in lots of five, being fed on a slatted platform with an inclined floor of sheet-zinc below it, so that the urine was drained into carboys containing acid, while the solid excretions were separately removed several times a day and preserved for analysis. The constituents determined in the food and in the manure in the experiments with oxen and sheep were dry matter, mineral constituents, and nitrogen, and in some cases woody fiber. As an illustration of some of the difficulties that must be overcome in making exact investigations of this kind, a more particular description of some of the devices resorted to will be of interest. "In the case of pigs, individual male animals were experimented upon, each for periods of three, five, or ten days only. Each animal was kept in a frame, which prevented it from turning around, and having a zinc bottom, with an outlet for the liquid to run into a bottle, and it was watched night and day, and the voidings carefully collected as soon as passed, which could easily be done, as the animal never passed either fæces or urine without getting up, and in getting up he rang a bell and so attracted the notice of the attendant. The constituents determined were, in the food and fæces, dry matter, ash, and nitrogen, and in the urine, dry matter, ash, nitrogen, and urea."

The amount and relative proportion of the different organs and parts of the body were determined in two hundred and forty-nine