THE FERMENTATION OF CELLULOSE 227 



a compound insoluble in water or weak acids and alkalis, 

 and under certain conditions can be hydrolysed into a 

 hexose sugar. Through mixture or combination with 

 other substances the cellulose of young cells becomes 

 greatly modified in its chemical and physical properties, 

 and a series of " compound celluloses " are formed. Thus 

 we have the pectocelluloses of cotton and flax fibres, and 

 the parenchymatous tissues in the flesh of turnips and 

 mangels which contain cellulose mixed or combined with 

 pectose : the adipocelluloses forming the cell-walls of cork 

 containing a waxy or fatty material suberin, and the 

 lignocelluloses of timber and lignified vessels and fibres in 

 the vascular tissues of all the higher plants. Paper is 

 composed of one or other of these celluloses obtained 

 from wood, straw or cotton and linen fibre. 



After the death of the plants, many of the celluloses 

 in them resist decomposition for a time, but sooner or 

 later they are hydrolysed to soluble carbohydrates, which 

 under aerobic conditions are finally oxidized to carbon 

 dioxide and water, the latter ultimately finding their way 

 back into the air and soil from which they were origi- 

 nally derived. This breaking down of cellulose is carried 

 out by certain bacteria and fungi, the end products of the 

 process being carbon dioxide and water where free and 

 abundant access of air is permitted. In situations where 

 the air-supply is restricted, as in the mud of marshes and 

 stagnant ponds, the cellulose is fermented by a number of 

 anaerobic bacteria and methane, or marsh gas (CH 4 ), 

 hydrogen and carbon dioxide are produced together with 

 small amounts of butyric and other fatty acids. The 

 gases are seen to rise in bubbles when the mud and 

 rotting vegetation at the bottom of a pond is stirred 

 with a pole or stick, and vessels completely filled with 



