100 CELLULOSE. 



of iodine after the action of chloride of zinc (Schulze's reagent). 1 

 These reactions afford a means of detecting cellulose. 



By treatment with strong sulphuric acid cellulose may be dis- 

 solved with the formation of a dextrin-like product: on diluting 

 with water and boiling it is finally converted into a sugar which 

 is apparently identical with dextrose. 2 



As already stated cellulose is undoubtedly digested in the ali- 

 mentary canal more especially of herbivora, but also to a less ex- 

 tent of man. 3 We know however but little of the real nature of 

 the digestive processes which are involved in this. Two views 

 are open to us. It has long been known that under the influence 

 of putrefactive organisms, as from sewer-slime, cellulose is disin- 

 tegrated and dissolved with an evolution of marsh-gas and car- 

 bonic anhydride. 4 This is usually known as the marsh-gas fer- 

 mentation of cellulose. In accordance with this it is possible that 

 a similar factor is at work in the alimentary canal, more especially 

 of the herbivora with their large caecum in which the food stays 

 for some time. This accords with the marked occurrence of marsh- 

 gas in the gases of their intestine and its increased presence in the 

 intestine of man when largely fed with a vegetable diet. 5 On the 

 other hand it is possible that the digestion may turn out to be due 

 to some definite enzyme, 6 but as yet no such enzyme has been 

 obtained with certainty from the secretions or tissues of the 

 alimentary canal. Possibly the organisms which as stated above 

 can cause the decomposition of cellulose do so by means of some 

 specific enzyme. It remains for further research to throw a 

 decisive light on the possibilities to which attention has been 

 drawn. 



Some difference of opinion exists as to the physiological sig- 

 nificance of cellulose digestion. There is at present no evidence 

 that the cellulose of food as such is a food-stuff in the same sense 

 that starch is. As far as the existing evidence goes we shall not 

 perhaps be far wrong in supposing that cellulose digestion is 

 primarily important as liberating from the cells the true food- 

 stuffs which they contain. At the same time the products formed 



1 The reagent used is prepared as follows. Iodine is dissolved to saturation in a 

 solution of chloride of zinc, sp.gr. 1 4 8, to which 6 parts of potassium iodide have been 

 added. See also Bower, Pract. Bot., 1891, p. 506. Cross and Bevan (loc. cit. p. 7) 

 recommend the following. Zinc is dissolved to saturation in hydrochloric acid, and 

 the solution evaporated to sp.gr. 2-0 ; to 90 parts of this solution are added 6 parts 

 of potassium iodide dissolved in 10 parts of water, and in this solution iodine is finally 

 dissolved to saturation. 



2 Flechsig, Zt. f. Physiol. Chem. Bd. vu. (1883), S. 523. 



3 Bunge, Phi/siol. and Path. Chem. 1890, pp. 81, 191. 



4 Popoff, Pfl'iiger's Arch. Bd. x. (1875), S. 113. Van Tieghem, Compt. Rend. T. 

 LXXXVIII. (1879), p. 205. Hoppe-Seyler, Ber. d. d. ckem. Gesell. Jahrg. xvi. (1883), 

 S. 122. Zt.f. physiol. Ch. Bd. x. (1886), Sn. 201, 401. 



6 Tappeiner, Ber. d. d. chem. Gesell. Jahrg. xv. (1882), S. 999 ; xvi. Sn. 1734, 1740. 

 Zt.f. Bid. Bd. xx. (1884), S. 52. (Gives literature to date.) Ibid. S. 215; xxiv. 

 (1888), S. 105. 



6 Hofmeister, Arch.f. Thierheilk. Bd. vn. (1881), S. 169; xi. (1885), Hfte. 1, 2. 



