Page:Popular Science Monthly Volume 65.djvu/191

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metabolism experiments with animals the amounts and composition of the food and of the urine and feces are the factors considered. Using this apparatus it is possible to determine the total income and outgo of both matter and energy. The apparatus affords opportunity for investigation in a great variety of important lines, and for checking the results secured by the more practical feeding experiments. It is especially adapted to studies of such questions, for example, as the energy required to digest and assimilate different classes of feeding stuffs, the food requirements of animals under different conditions, and the replacing value of nutrients.

An experiment recently reported with the apparatus, the first one to be published, was on the available energy of timothy hay. In this a large steer was used, and there were four periods, each covering two days in the respiration chamber. This first experiment gave results of much interest from both a scientific and a practical standpoint, and clearly demonstrates that for studies on the nutrition of animals, as well as of man, the possible lines of investigation with the respiration calorimeter range from the most practical to the most technical subjects.

It is worthy of mention that the Armsby-Fries apparatus is a distinctly American product, and is the only one of its kind in operation in the world. A similar apparatus, modeled after it, is being constructed at the agricultural academy in Bonn, Germany, but is not yet in operation.