FERMENTATION OF CELLULOSE 785 



tremely polymorphic, each being capable of assuming the shape 

 of short rods, long rods, and irregularly distended involution 

 forms. 



The cementing gelatinous portion of the zooglcea in Bacterium 

 xylinum consists of cellulose, and the organism can form this 

 substance from the sugars dextrose and levulose. 



6. Fermentation of Cellulose. — A large portion of the 

 cellulose contained in the tissues of plants disappears in 

 the passage through the alimentary canal of cows, horses, 

 sheep, and other herbivorous animals. Formerly it was 

 thought that the dissolution and destruction of the cellulose 

 under these circumstances was due to the action of enzymes 

 concerned in the ordinary process of digestion : it is now 

 known, however, that a great part of the decomposition is 

 brought about by bacteria present in the first stomach 

 and intestines of these animals. The cellulose is split up 

 chiefly into carbon dioxide and methane or marsh-gas (CHJ, 

 but small quantities of hydrogen, acetic, butyric and other 

 acids are produced at the same time. The fermentation 

 can be carried on outside the body of the animal when 

 nutrient solutions containing cellulose are inoculated with 

 a small portion of the contents of a herbivorous animal's 

 colon. 



The process also goes on in dung-heaps, the necessary con- 

 dition for the most vigorous activity of the bacteria concerned 

 in it being an adequate degree of moisture, absence of air, and 

 a temperature between 40° and 5°° C. 



The same or a similiar type of fermentation takes place in 

 silage, and also among the plant-debris present on all soils and 

 in the mud of swamps and stagnant ponds : much of the marsh- 

 gas and carbon dioxide produced rises in conspicuous bubbles 

 when the mud at the bottom of a stagnant pool is stirred up 

 with a stick. 



3D 



