The real value of the two rations per unit is thus shown to 

 have been the same. The economic advantage of the second was 

 not due to any higher nutritive value, but simply to the fact that 

 more of it was eaten. Similarly, if we suppose the foregoing re- 

 sults to have been obtained, not with two different rations but 

 with two different animals on the same ration, the experiment does 

 not show that the second animal digested or assimilated his feed 

 any more efficiently than the first but simply shows the economic 

 advantage of a larger consumption of feed. It scarcely need be 

 added that the same principle applies in all cases of productive 

 feeding, as has recently been shown in a very striking manner by 

 Eckles 1 in experiments upon dairy cows. 



THE MAINTENANCE REQUIREMENTS. 



Unlike the operations of a factory, which cease when the power 

 is shut off, the activities of the animal do not stop when food is 

 withdrawn, but continue for a variable length of time at the expense 

 of the tissues of the body. Men have fasted voluntarily for 30 days 

 or more without obvious permanent ill effects and there are records 

 of dogs having survived fasting periods of from 60 to 90 days. In the 

 fasting animal at rest, the vital activities are reduced as it were to 

 their simplest terms, practically only those functions being active 

 which are essential to continued life. In such a fasting animal the 

 power necessary to operate the machinery of the body is derived from 

 the breaking down and oxidation of the materials of the body. It is 

 as if the materials of the factory itself were being cut up and used 

 as fuel under the boilers. 



Scientific investigation confirms common observation in show- 

 ing that it is chiefly the fat of the body which is used in this way. 

 Fat is the body's surplus of fuel material, laid aside when food is 

 abundant in order to serve precisely this purpose in time of scarcity. 

 The gradual emaciation of the fasting or insufficiently fed animal 

 is too familiar to require more than mention. 



But while the body fat is usually the chief material used up by 

 the fasting animal, it is not the only one. As is well known, the 

 active tissues of the body consist chiefly of protein and it appears 

 that all their activities are necessarily accompanied by the breaking 

 down and oxidation of more or less of their protein, so that the 

 fasting animal is continually losing protein as well as fat. If the 



1 Missouri Experiment Station, Research Bulletin Iso. 2. 



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