6 5 8 



NUTRITION OF FARM ANIMALS 



per kilogram live weight the results shown in Table 199, which are 

 stated in a form somewhat different from that used by Rubner but 

 which in substance are identical with his. 



These figures- appear somewhat remarkable in view of the fact 

 that the comparison is virtually with body fat. Literally inter- 

 preted, it means that the energy of feed fat is only 87 per cent as 

 valuable for maintenance as the energy of mobilized body fat plus a 

 little protein. If this be true, it implies a larger expenditure of 

 energy in the digestion of fat or a greater stimulating effect of the 

 resorbed fat upon cell activity than now seems probable, since the 

 katabolism of resorbed feed fat can hardly differ greatly from that of 

 body fat. Rubner's figure is the result of a single experiment and 

 unfortunately it enters into the computation of all the other results. 

 It is a matter of much interest, therefore, that Lusk 1 has found a 

 much lower heat increment for fat. In two calorimetric experiments 

 in which an emulsion of olive oil was given to a dog he found the 

 additional heat elimination to be 0.92 per cent and 1.49 per cent 

 of the energy of the oil, so that on the average 98.8 per cent of energy 

 of the fat was available for maintenance, a much higher figure than 

 Rubner's. 



Both Rubner and Lusk find the most marked effect to be produced 

 by protein. In two other experiments by Rubner an amount of lean 

 meat nearly sufficient to maintain the dog was fed. The meat con- 

 tained a small amount of fat, the average metabolizable energy of 

 the feed per kilogram live weight being as follows : 



In protein 56.70 Cals. 



In fat 4.95 Cals. 



61.65 Cals. 



Using the data afforded by the experiment on fat, the heat incre- 

 ment due to the protein may be computed as follows : 



TABLE 200. INCREMENT or HEAT PRODUCTION BY DOG ON MEAT DIET 



Jour. Biol. Chem., 13 (1912), 38. 



