128 THE CARBOHYDRATES 



hours ; it is then washed, first with water, and, finally, with 

 2 per cent solution of acetic acid. The cellulose is thus dis- 

 solved and fills the cells and intercellular spaces. On treat- 

 ment with chlorzinc iodide the middle lamella gives either no 

 colour reaction or turns a pale yellow, while the cellulose gives 

 the familiar blue reaction ; the membrane stains very deeply 

 with safranin or methylene blue, and is easily soluble in a 

 solution of ammonium oxalate. 



REFERENCES. 



O'Sullivan: "J. Chem. Soc, Lond," 1884, 45, 41; 1890,57,59; 1891,59, 

 1029; 1901, 79, 1 164. 



H. H. Robinson : " Brit. Ass. Reports, York," 1906, 227. 



CELLULOSE. 



The term cellulose should be taken in general to connote a 

 group of substances rather than a single chemical compound ; 

 used in this generic sense, it comprises a number of substances 

 of somewhat different origin and somewhat different characters, 

 whose chief common properties are their physiological origin 

 and their function in forming the basis of the material which is 

 isolated by the protoplasm of the living cell for the purpose of 

 forming the wall or periphery of that cell. Though met with 

 chiefly in the vegetable kingdom, its occurrence in the animal 

 kingdom is not unknown, since a substance described as Tunicin, 

 said to be identical with cellulose, has been found in the cell 

 walls of certain Tunicates and insects. In the course of time 

 the cellulose originally formed is altered by the addition to it 

 of various secondary products known as encrusting substances ; 

 thus the process of lignification consists in the conversion of 

 cellulose into ligno-cellulose ; accompanying this change is a 

 gradual disappearance of the protoplasm. Thus the proto- 

 plasm within the cell produces a number of different substances 

 which are deposited in the cell wall, the nature and properties 

 of the resulting fibre depending, of course, on the nature of 

 these substances. 



CLASSIFICATION OF CELLULOSES. 



The naturally occurring celluloses may be divided into the 

 following groups : — 



