THE PRODUCTION VALUES OF FEEDING STUFFS 637 



vidual difference in this respect between animals. Recently 

 Zuntz and his associates x have reported striking instances in 

 which the extent of the methane fermentation in particular 

 has been markedly affected by the make-up of the rations and 

 especially by the order in which the feeds were consumed, while 

 Voltz and his associates 2 have laid much stress upon the prac- 

 tical importance of these results. No such marked differences 

 were observed in Armsby and Fries' experiments but the range 

 of feeding stuffs used was not so wide. It is perhaps too early 

 to judge of the full significance of Zuntz' s results, but they should 

 at least serve to correct the notion, more or less subconsciously 

 held by not a few, of digestion as a perfectly definite process 

 and of a digestion coefficient as a sort of chemical constant. 

 On the other hand, however, it seems quite possible to over- 

 estimate the effect of such variations in the digestive process 

 upon the net energy values of feeding stuffs. On the whole, 

 they appear to be of far less significance than other factors to 

 be considered later. 



The percentage of the gross energy which is lost in the fer- 

 mentation gases, as appears from Table 188 (749), is not usually 

 very large. It is naturally greatest in the case of feeding stuffs 

 rich in carbohydrates, especially the easily soluble carbohydrates. 



745. Computation of fermentation losses. While the ex- 

 perimental determination of the energy losses in feces and 

 urine is a comparatively easy task, requiring relatively simple 

 appliances, the determination of the fermentation losses neces- 

 sitates the use of the somewhat complicated and costly res- 

 piration apparatus. In the absence of such an apparatus, how- 

 ever, it is possible to compute the fermentation losses with a fair 

 degree of accuracy from the results of the ordinary digestion 

 experiment. The methane fermentation attacks chiefly or 

 wholly the carbohydrates (135, 140) and in the case of cattle, in 

 particular, it has been shown that the amount of methane pro- 

 duced is in general proportional to the amount of total car- 

 bohydrates (crude fiber and nitrogen-free extract) digested. 



Kellner 3 in forty-four experiments with cattle on mixed 

 rations found the average methane excretion to be 4.2 grams 



1 Landw. Jahrb., 44 (1913), 765 ; Landw. Vers. Stat., 79-80 (1913), 781. 



2 Landw. Jahrb., 44 (1913), 685 ; 45 (1913), 325. 

 8 Landw. Vers. Stat., 53 (1900), 415. 



