170 CHEMICAL COMPOSITION. [BOOK n. 



exhibited its usual composition. A similar examination was 

 made of the purified membrane of other plants, and always 

 with the same result, showing that cellulose itself is uniform 

 in its composition, and that all seeming variations in it are 

 owing to the presence of azotised matter of various kinds, 

 deposited on the surface of the membrane, and not penetrating 

 into its interior. 



