44 Journal of Agrictdtural Research voi. xiii, no. i 



METHODS OF EXPERIMENTATION 



The determination of the fasting katabolism of animals such as Carni- 

 vora, man, or swine, having a comparatively simple apparatus, is largely 

 a question of experimental technic. With ruminants the case is dif- 

 ferent. Their digestive apparatus is capacious and complicated, and 

 contains at all times a relatively large amount of feed in process of diges- 

 tion. It seems scarcely possible by any moderate period of fasting to 

 reach a condition corresponding to the postresorptive state in man or 

 Carnivora. The fasting katabolism may, however, be obtained indi- 

 rectly by a comparison of the total metabolism on two different amounts 

 of the same feed in the manner described in previous publications (i, p. 

 55; 2, p. 282; J, p. 53; 6, p. 460)} For example, a steer receiving two 

 different amounts of the same mixed ration gave the following results: 



Item. 



Period 2 , 

 Period I , 



Difference 



Heat increment per kilogram of dry matter. 



Dry matter 

 eaten daily. 



Kgm. 

 9. 146 

 4-463 



4.683 



Daily heat 

 production. 



Calories. 

 16,511 

 10, 905 



5, 606 



Evidently, out of the total metabolism of 10,905 Calories in period i, 

 1,197X4.463 = 5,342 Calories maybe regarded as the heat production 

 caused by the 4.463 kgm. of dry matter eaten, while the remainder, 

 5,563 Calories, is the basal katabolism. 



Strictly speaking, the foregoing method of computation assumes that 

 the heat production caused by the feed is a linear function of its amount. 

 This can not be regarded as having been proved, but no distinct indica- 

 tions to the contrary have appeared within the range of our experiments, 

 while Wood and Yule (21, p. 239) compute that in Kellner's respiration 

 experiments on fattening cattle the gains expressed in terms of energy 

 are proportional to the metabolizable energy supplied in excess of 

 maintenance, which, of course, is equivalent to saying that the heat 

 production is also a linear function of the feed supply. 



Our investigations on the metabolism of cattle afford data for a number 

 of computations of the basal katabolism. Full statements regarding the 

 methods employed, the animals used, the feed consumed, etc., have 

 already been published {4, 5,6,7). The designations of the experiments, 

 animals, and periods in the following pages correspond with those in the 

 publications cited. 



In view of the very striking effect of standing in increasing the metab- 

 olism of cattle the basal katabolism per 24 hours has been computed 



' Reference is made by nimiber (italic) to "Literature cited," pp. s5-57- 



