196 BUTYRIC ACID FERMENTATION. 



1884, who showed the fate of all cellulose taken into the body and 

 not evacuated in the faeces to be, not digestion and absorption into- 

 the arterial circulation, but fermentation into marsh-gas. The 

 operation, however, does not proceed exactly according to the 

 above equation, but yields, in addition to methane, volatile fatty 

 acids (chiefly acetic acid, then butyric acid, &c.). Bearing this 

 in mind, this decomposition process cannot be regarded as totally 

 without value for the animal body, although, naturally, the co- 

 efficient of digestibility, hitherto usually assumed, necessarily 

 suffered considerable depreciation. Moreover, this process is in- 

 directly favourable, in so far that, by the solution of the cell- walls, 

 the cell contents of the vegetable nutriment are laid bare, and thus- 

 rendered more readily accessible to the digestive fluids. Although 

 by this discovery the chief source of the intestinal gases so 

 copiously evacuated by herbivorous animals is made manifest, still 

 it should not be assumed that the methane therein is exclusively 

 derived from the fermentation of cellulose, since Huge and Planer 

 proved that, even in cases of a purely flesh diet, methane is to be 

 found in the intestinal gases (of man and the dog). 



Cellulose fermentation also plays a part in the preparation 

 of brown hay, sweet ensilage, and sour fodder, considered in 

 Chapter xxvii., where it forms one of the causes of the great loss 

 of matter inherent in these processes, in connection wherewith 

 reports have been made by Weiske, 0. Kellner, M. Maercker, 

 and others. This process also goes on as shown in 1884 by 

 P. DEHERAIN (I.) and U. GAYON (I.) in manures. If, favoured 

 by special circumstances, it proceeds more rapidly than the decom- 

 position of all the other (and especially the nitrogenous) con- 

 stituents, then an irregularly fermented product deficient in the 

 fibres necessary to impart porosity to the mass and known as- 

 fatty manure, is the result. 



The evolution of marsh-gas and hydrogen by the agency of 

 bacteria also occurs, not infrequently, in other situations ; for 

 instance, in the diffusers in sugar works, and very often so strongly 

 that the amount of gas suffices to produce powerful explosions 

 when the diffusers are incautiously approached with a naked light. 

 The teaching of experience, that frozen beet is particularly liable 

 to such a form of decomposition, is probably explicable by the 

 circumstance that such beet cannot be entirely freed from adherent 

 particles of soil, and the ferments present therein. It is also con- 

 ceivable that, by the agency of frost, the pectins in the beet are 

 transformed into a more readily decomposable condition. On this 

 point a few observations have been made by Millot and Maquenne, 

 and, more recently, by P. DEHERAIN (II.); more accurate investi- 

 gations thereon are, however, still lacking. 



