Page:Popular Science Monthly Volume 79.djvu/505

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501
THE FOOD SUPPLY

calorimeter under the constant observation night and day of three or four skilled men. Its intake of food and energy, the losses in the excreta, the volume, composition and temperature of the air passing through the apparatus and in the case of the respiration calorimeter especially the temperature of the water used to take up the heat produced are matters of continuous record. A single "run" with the latter apparatus involves the recording of nearly 7,000 observations, while fully 25 samples of various sorts are taken whose subsequent analysis in the chemical laboratories involves the making of some 150 determinations.

From the results of these hundreds of weighings, records and analyses there is finally worked out a complete balance of income and outgo.[1] Comparisons of these balances on different amounts and kinds of feed, with different animals, and under varying conditions, permit exact conclusions to be drawn regarding the nutritive effects of the rations consumed.

The investigations in progress relate to three different aspects of the general problem: First, how do different feeding stuffs compare with each other as to their content of energy and the proportion of it which is available to the animal? Second, what is the relative efficiency of different types of animals as converters of waste energy into human food? Third, how do the various conditions under which animals may be kept affect their efficiency in this respect? To the extent to which it becomes possible to answer these questions for the different species of farm animals we shall possess the scientific basis for a rational system of conserving to the utmost for man's use the energy which the studies of the chemist, the physicist, the botanist, the agronomist and the soil expert have taught the farmer how to accumulate in his crops. The investigations are, therefore, in reality a study of the conservation of the food supply, a problem even more fundamentally important than the conservation of our mines, forests or water powers, and one which vitally concerns the welfare not of the farmer alone but of the whole people.

  1. On page 500 is an example of such a balance sheet.