CELLULOSE. 269 



digestion, and the comportment of different substances while 

 subjected to this process, we have nothing to add to the observa- 

 tions already made, excepting to remark that we shall not here 

 have to notice the digestive fluids with which these groups of 

 substances are brought in contact, since these substances pass 

 from the intestinal canal into the mass of the juices in the same 

 unchanged state in which they entered it. The combinations into 

 which some of these substances enter with acids during the process 

 of digestion, can scarcely come within the scope of the present 

 inquiry, since no essential change is produced by their action. 



In turning to the consideration of the individual objects of 

 digestion, our attention is in the first place directed to a group of 

 substances which have been distinguished by the irrational name 

 of the carbo-hydrates, amongst which are included cellulose, the 

 different kinds of gum, starch, inulin, lichenin, and the different 

 kinds of sugar. 



It must be observed, in reference to cellulose or the substance 

 of the vegetable cell, that it belongs to those substances which 

 resist all the digestive fluids and other solvents ; and_, on account 

 of this property, all those vegetable substances which essentially 

 consist of this substance re-appear unchanged in the excrements 

 of herbivorous and omnivorous animals. It must, however, be 

 borne in mind that this substance (which Mitscherlich,* in his 

 more recent experiments, found to be perfectly isomeric with 

 starch and is represented by the formula C 12 H 10 O 10 , although 

 its composition had been previously assumed by Mulder to be 

 C 24 H 21 O 21 ) is very frequently found to be incrusted with some 

 other perfectly insoluble substance, such as lignin or suberin. 

 When, as in the case of the Beaver, we find the whole stomach, 

 and more especially the caecum, plugged, as it were, with fragments 

 of wood and bark, without being able at the same time to detect 

 any easily soluble nutrient substances as, indeed, E. H. Weberf 

 and myself have frequently observed we can scarcely avoid 

 adopting the opinion that the digestive juices, at all events, of 

 these animals, are capable of exerting a metamorphic and solvent 

 action upon cellulose. This view of the subject seems also to 

 gain confirmation from a circumstance especially noticed by 

 E. H. Weber,J that in the beaver, those organs whose secretions 

 more especially contribute towards the metamorphosis of the 



* Ann. d. Ch. u. Pharm. Bd. 75, 8. 305-314. 



t Ber. d. konigl. sachs. Gesellschaft d. Wiss. 1850, S. 192. 



% Ibid, p. 193. 



