258 NUTRITION OF FARM ANIMALS 



complete rest and at moderate external temperature, the vital 

 activities are evidently reduced to the minimum compatible 

 with the continuance of life. Since the internal work of such 

 an animal is performed at the expense of the chemical energy 

 stored up in its tissues, the body's stock of energy is being 

 constantly depleted by an amount equivalent to the internal 

 work done and this loss of energy must be made good from the 

 feed if the animal is to be maintained. The relatively constant 

 total katabolism of the fasting animal, as expressed in its heat 

 production, is therefore the measure of the amount of energy 

 expended in carrying on the fundamental vital activities of 

 the body, and consequently of the minimum quantity which must 

 be supplied in a maintenance ration. 



3. CONDITIONS AFFECTING THE FASTING KATABOLISM 



345. Size of animal. That large animals katabolize more 

 matter and produce more heat than smaller ones, and therefore 

 require more feed for maintenance, needs no special proof. Ex- 

 periment shows, however, that the difference is not propor- 

 tional to size or weight, but that small animals have a more 

 intense katabolism than large ones, its amount being approxi- 

 mately proportional to the body surface, which, of course, is 

 relatively greater in the smaller animal. 



The relation to body surface appears to have been first suggested 

 by Bergmann (cited by Rubner) in 1852 and later by Miintz l in 1878, 

 but Rubner 2 seems to have made the first quantitative investigation 

 of the question, determining the fasting katabolism of six dogs whose 

 weights ranged from 3 to 24 kilograms. 



While not mathematically constant, the ratio between the fasting 

 katabolism and surface showed a close approximation to uniformity, 

 and the same fact has been verified by a considerable number of in- 

 vestigators, although with some exceptions, and is now generally ac- 

 cepted. Moreover, it has been shown 3 to be approximately true not 

 only of animals of the same species but of animals ranging in size 

 from man to domestic fowls and including also cold blooded animals. 



346. Computation of katabolism per unit of surface. It 

 is a familiar fact that the surfaces of solids of the same shape, 



1 Ann. Inst. Agron., Ill, p. 59. 2 Ztschr. Biol, 19 (1883), 535. 



3 E. Voit; Ztschr. Biol., 41 (1901), 113. 



