276 NUTRITION OF FARM ANIMALS 



in cattle does not contribute very largely to the increased heat 

 production consequent on the consumption of feed. 



b. Glandular activity. The increased metabolism required 

 for the secretion of the digestive fluids and for the excretion of 

 metabolic products is also to be reckoned among the causes of 

 the heat production consequent on the ingestion of feed. 



c. Fermentations. The extensive fermentations, especially 

 the methane fermentation, occurring in the digestive tract of 

 herbivora (128-130, 132) result in a considerable evolution of 

 heat. No entirely satisfactory determinations of its amount 

 have yet been reported, but Von der Heide, Klein and Zuntz 1 

 compute from MarkofTs experiments that the methane fer- 

 mentation in cattle gives rise to the evolution of 4.374 Cals. of 

 heat per cubic centimeter of methane, equivalent to 6.07 Cals. 

 per gram. 



d. Intermediary metabolism. The chemical changes which 

 the nutrients undergo during digestion and resorption and 

 especially in the intermediary metabolism (compare Chapters 

 III and V) have been invoked to explain the increased heat 

 production consequent on the consumption of feed, particularly 

 of protein, but apparently without sufficient warrant, most 

 of these reactions seeming to be substantially isothermic. 



e. Direct stimulus to metabolism. Recent investigations by 

 Lusk and his associates 2 upon the cause of the specific dy- 

 namic action, together with earlier experiments by Gigon, 3 

 have gone far towards clearing up the subject. According to 

 Lusk, the action of carbohydrates and fats is to be explained 

 substantially as was done by C. Voit in 1881, viz., as the direct 

 effect of a greater supply of non-nitrogenous material to the 

 cells, i.e., as virtually a case of mass action. The products of 

 protein katabolism, on the contrary, particularly the hydroxy 

 and keto-acids resulting from the deaminization of the amino 

 acids (233), act as direct stimuli to the katabolism of non- 

 nitrogenous matter in the body cells. 



That these actions play their part, along with mechanical 

 work and fermentations, in bringing about the increased heat 



1 Landw. Jahrb., 44 (1913), 70S- 



2 Jour. Biol. Chem., 12 (1912), 349; 13 (1912), 27, 155, 185; 20 (1915), 555- 

 Proc. Internat. Cong. Hygiene, 1913. Arch. Inter. Medicine, 12 (1913), 485. Jour. 

 Amer. Med. Asso., 63 (1914), 824. 



3 Skand. Arch. Physiol., 21 (1909), 351 ; Arch. Physiol. (Pfliiger) , 140 (1911), 548. 



