CHAPTER XXXI 



CELLULOSE FERMENTATION 



Cellulose is a substance closely related to starch 

 and sugar. It enters into the composition of the cell- 

 walls of all plants and is familiar to us as a material 

 resistant to decay. Wood, paper and straw are all rich 

 in cellulose, while cotton and flax fiber, and, particularly, 

 Swedish filter paper, contain it in almost pure form. 

 When plant substances undergo decay, the cellulose 

 usually resists the attacks of bacteria for a longer time 

 than do the starches, sugars and proteids. However, 

 under certain conditions, it may be dissolved by micro- 

 organisms and converted into a mixture of gaseous and 

 solid products. 



Because of its inert nature, cellulose is not readily 

 digested by animals. Foods rich in "crude fiber" possess, 

 therefore, a lower degree of digestibility than foods with 

 a small proportion of it. At the same time, herbivorous 

 animals are, to a greater or less extent, endowed with 

 the ability to digest cellulose, as was already observed 

 by Haubner in 1855. In 1875, it was announced by 

 Popov that the marsh gas observed to issue from cess- 

 pools and swamps was derived from the fermentation 

 of cellulose. This led to the suggestion that the marsh 

 gas known to form a portion of the gases in the intestinal 



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