COMPOSITION OF FEEDING-STUFFS 13 



true quantity of crude fibre is obtained. Crude 

 fibre obtained in the above manner is free from 

 nitrogen, and consists of a mixture of cellulose 

 pentosans, lignin, and cutin. 



Cellulose is closely related to starch in its chemical 

 composition, and is found in an almost pure state 

 in cotton-wool which has been freed from fat. 

 Like all the components of the crude fibre it is in- 

 soluble in water and dilute acids and alkalies. 

 Strong acids (sulphuric, hydrochloric), on the other 

 hand, attack it and convert it into glucose. 



The pentosans have not yet been prepared in a 

 pure form. Their presence in crude fibre is inferred 

 from the fact that on boiling this portion of the 

 plant with dilute acid, characteristic pentose sugars, 

 such as xylose, are formed. The pentosans must 

 be regarded as being the mother substance of these 

 sugars. 



Cellulose and the pentosans have the same per- 

 centage composition (44-4% carbon), whilst lignin 

 and cutin, which are less well known, are richer in 

 carbon, the former having 55-60%, and the latter 

 68-70%. The components of the crude fibre are 

 so intermingled that the particles of cellulose and 

 the pentosans may be embedded in the cutin and 

 lignin. These two compounds are often grouped 

 together as " incrusting materials." The higher 

 the percentage of lignin and cutin in the crude 

 fibre the closer does it approach wood in its pro- 



