270 DIGESTION. 



carbo-hydrates are developed in a remarkable degree; thus, for 

 instance, the salivary glands are exceedingly large in the Beaver, 

 amounting, according to Weber's estimate, to 1-1 18th of the whole 

 weight of the body, whilst in man, for instance, they do not 

 exceed the l-895th part of the entire weight. In the same 

 manner the pancreas is remarkably voluminous in the Beaver 

 {Weber found that it measured 18 inches in the case of a tolerably 

 large animal). It seems more doubtful, whether the well-known 

 large gastric gland, which is peculiar to the Beaver, bears a direct 

 relation to the animal's digestion of cellulose. If we should be 

 disposed to ascribe to the secretions of this apparatus, which exert 

 so powerful an action on starch, the property of converting 

 cellulose into dextrin and sugar, it must, at least, be admitted that 

 the chemical relations of cellulose to certain solvent and meta- 

 morphic agents are in no respect opposed to this view. It is a 

 well-known fact, which was first observed by Schleiden, and has 

 been admirably elucidated by Mulder, that cellulose, by treatment 

 with the second or third hydrate of sulphuric acid, is converted 

 into a substance very similar to starch, and which is coloured 

 blue under the action of iodine. According to Mulder, syrupy 

 phosphoric acid may, in such cases, be used in place of the sul- 

 phuric acid. Notwithstanding the acid nature of the contents of 

 the stomachs of Beavers, and however much this large gastric 

 gland seems to imply that the free acid is destined for the meta- 

 morphosis of the cellulose, the acids which occur here are always 

 too much diluted to justify us in ascribing to them such a meta- 

 morphic action. At any rate, on an accurate micro-chemical 

 investigation of the fragments of wood, bast, and bark found in 

 the stomach and duodenum of the Beaver, I have never been 

 able to perceive that the addition of iodine induced a blue 

 colouration in the cellulose fibres and cells, although this colour 

 always appeared very beautifully after repeated applications of sul- 

 phuric acid. The alkaline juices of the salivary glands, the 

 pancreas, and the csecal glands, probably exert a stronger influence 

 on the conversion of cellulose into starch, and its further decom- 

 position into sugar, than the acid juices of the stomach. For 

 the admirable experiments of Mitscherlich* show us that even 

 very dilute alkaline solutions act upon cellulose, whilst con- 

 centrated solutions act more readily and completely than con- 

 centrated acids in converting this substance into starch. Hence we 

 must suppose that the greater part of the cellulose undergoes its 



* Op. cit. 



