214 THE CARBOHYDRATES 



AF represents the glucose anhydride unit of cellulose, the 

 dashes representing oxygen linkages ; by oxidation the alde- 

 hydic group B is developed from A and on further oxidation 

 gives the carboxyl group C ; hydrolysis at F then sets free 

 the glucuronic acid. 



Microchemical Detection of Oxycellulose. — The investiga- 

 tions of Wood * and of Mehta f have shown that oxycellulose 

 occurs naturally in the cell wall of a great variety of plant 

 materials, and may be detected by the following means : — 



The material is washed with acid and then with water to 

 remove all acid and then is stained with congo red ; by 

 treating again with acid, the red colour is changed to blue ; 

 on washing with water until the background becomes red, 

 any oxycellulose present will appear dark blue or black. 

 Oxycellulose, in common with pectic substances, hemicellu- 

 loses, and gums is stained by ruthenium red. 



CONSTITUTION OF CELLULOSE. 

 While it is agreed that cellulose is built up from a number 

 of glucose anhydride groups C^^qO^ opinions differ as to the 

 constitution of this unit group. The formulae proposed by 

 Cross and Bevan, Vignon, and Green are given below : — 



CH COH CO CHOH— CH— CHOH 



CHOH CHOH CHOH CHOH CHOH CHOH 9 ^ 

 CHOH CHOH CHOH CHOH °' CHOH CHOH ^HOH-CH— CH, 



COH CH CH, 



Cross and Bevan's formulae.i Green's formula.^- 



O CH— CHOH 



I I 



O CHOH 



CHj— CH— CHOH 



Vignon's formula.Jl 



Cross and Bevan's formula implies the presence of a ketonic 



group for which there is no evidence ; furthermore it contains 



* Wood : " Ann. Bot.," 1924, 38, 275 ; 1926, 40, 547. 



t Mehta : " Biochem. Journ.," 1925, 19, 979. 



t Cross and Bevan : "J. Chem. Soc," 1901, 79, 366. 



§ Green and Parkin : id., 1906, 81, 811. 



II Vignon : " Bull. Soc. Chim.," 1899, 21, 599. 



