THE FOOD SUPPLY 501 



calorimeter under the constant observation night and day of three or 

 four skilled men. Its intake of food and energy, the losses in the ex- 

 creta, 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 pro- 

 duced 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 an- 

 alyses 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 ra- 

 tions 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. 



