100 CELLULOSE. 



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

 These reactions afford a means of detecting cellulose. 



By treatment with strong sulphuric acid cellulose may be dissolved 

 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 extent 

 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 disintegrated and dissolved 

 with an evolution of marsh-gas and carbonic anhydride 4 . This is 

 usually known as the marsh-gas fermentation of cellulose. In accord- 

 ance 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 significance 

 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 



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

 a solution of chloride of zinc, sp. gr. 1 '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. Ghem. Bd. vn. (1883), S. 523. 



3 Bunge, Physiol. and Path. Ghem. 1890, pp. 81, 191. 



4 Popoff, Pfliiger's Arch. Bd. x. (1875), S. 113. Van Tieghem, Comp. Rend. T. 

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

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



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

 1740. Zt. f. Biol. 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. 



