643 



and the digestibility of the substances. This is more or less true of 

 both nitrogvnous and non-nitrogenous compounds. [It is of course 

 understood that the fermentations here referred to are in general those 

 which are caused by bacteria and other so-called organized ferments, 

 and which result in more or less of cleavage and kindred cliemical 

 changes, such as the formation of lactic and acetic acids from carbohy- 

 drates and of amide-like compounds from albuminoids. Such changes 

 as those of starch into glucose and albuminoids into peptones would not 

 be included,] 



As regards the effects of the fermentations upon the digestibility of 

 the non-nitrogenous compounds, categorical conclusions are rendered 

 difficult by the lack of convenient and accurate methods for the deter- 

 mination of digestibility. "This much, however, may in general be 

 atlirmed: When a mixture of digestible and undigestible non-nitrogen- 

 ous extractives is exposed to organisms which cause fermentation and 

 putrefaction, the more easily soluble and digestible {;om])ounds are the 

 first to be decomixtsed and hence are most exi^osed to loss. The infer- 

 ence is that the non-nitrogenous extractives which remain and which 

 have been less influenced by the fermentation must contain relatively 

 larger i)roportions of the un<ligestible constituents than would be con- 

 tained in the whole of the given group of non-nitrogenous constituents 

 in the fresh or properly dried [material]." 



Another source of loss of feeding value in fermentation is the loss of 

 potential energy. "A part of the non -nitrogenous extractives is changed 

 into fermentation products. Here the law api^lies that the potential 

 energy of the products of a fermentation which is accompanied by the 

 evolution of heat is less than the potential energy of the original sub- 

 stance by the amount of heat involved. For this reason the residual 

 l^roducts must have a lower nutritive value, and in this sense the fer- 

 mentation of the feeding stuff must diminish its value." 



If the fermentation is carried far enough there may not only be a loss 

 of nutritive value from the diminution of iiotential energy, but the 

 residual products may become injurious rather then nutritious, as in 

 the formation of acetic and other acids from starch and sugar. " Unfor- 

 tunately the nutritive values of the most important products of fer- 

 mentation are not known with enough certainty to permit the statistical 

 expression of this loss. It appears from the experiments of Weiske 

 [see Experiment Station Eecord, vol. ii, p. 681], however, that the 

 actual nutritive value of acetic and butyric acid is very small, since 

 addition of acetic acid to the food [of rabbits and sheep] exercised an 

 unfavorable rather than a favorable action upon the formation of flesh 

 [storage of protein] ; more nitrogen was excreted with the acetic acid 

 than without it. On the other hand, with lactic acid in small quanti- 

 ties Weiske found the nitrogen storage to be somewhat increased." It 

 is evident then that the organic acids formed by fermentation must 

 have far less feeding value than the carbohydrates from which they are 

 produced, and that they may be positively detrimental. 



