64 Cellulose 



cellulosic structures, the remainder having been dissipated 

 and restored to the general fund of matter in circulation, in the 

 gaseous form viz. as CO 2 and CH 4 . 



(3) In the processes of animal nutrition plants and vegetable 

 substances are, of course, most important factors. In the course 

 of animal digestion the vegetable substances are attacked by 

 the fluids of the alimentary tract and resolved into proximate 

 constituents fulfilling the requirements of the organs of assimi- 

 lation ; and in addition to these decompositions, which are 

 largely hydrolytic in character, more fundamental resolutions 

 are observed in which the carbohydrate molecules are com- 

 pletely broken down, i.e. with formation of gaseous products. 



Processes of the first of these three groups are well known 

 to plant physiologists ; tissues of a cellulosic character are 

 specialised to serve as reserves of nutrient material, or reserve 

 material is stored up within a cellulosic cell wall which requires 

 to be broken down in order that the supply may be liberated. 

 In the seeds of the Gramineae, more especially the barleycorn, 

 this process of reabsorption of a cellulosic tissue has been care- 

 fully studied, and there is no doubt that the process of breaking 

 down the cellulose is due to the action of a special ferment a 

 cellulose-dissolving enzyme. It must be noted here that the 

 celluloses susceptible of this simple form of hydrolysis are ol 

 very different constitution from the typical cotton cellulose, 

 and the features of this differentiation will be discussed subse- 

 quently. Taking cellulose, however, as a general expression 

 for the colloid carbohydrates, we may regard them as having 

 the property of yielding to the hydrolytic activity of special 

 enzymes. 



As the student is now considering ferment actions he may take, 

 in illustration of these general views, the alcoholic fermentation of 

 dextrose. The main products of this decomposition alcohol and 

 carbonic acid are so related that the decomposition may be ex- 

 plained as resulting from migration of oxygen in the one, and of 



