1 82 THE CARBOHYDRATES 



hydrolysed by certain bacteria to mannose and a trisaccharide 

 mannotriose, and Paton, Nanji, and Ling * have found that 

 the nuts themselves contain an enzyme capable of hydrolysing 

 the mannan to mannose with probably the intermediate 

 formation of mannotriose. 



A substance known as yeast gum, which occurs in consider- 

 able quantities in yeasts of weak fermenting power.f is also 

 a mannan ; the amount of this substance present in yeast is 

 in inverse proportion to the amount of glycogen (cf. p. i68), 

 but it is not regarded as a reserve substance ; its solution, 

 which has a strong foaming power in water, does not reduce 

 Fehling's solution. 



PARAMANNAN. 



Paramannan is a variety of mannan which is characterized 

 by being much more resistant to hydrolysis ; this substance, 

 which is contained in coffee beans, is only slightly acted on by 

 hot dilute mineral acids, potassium chlorate, and hydrochloric 

 acid, but dissolves in a concentrated hydrochloric acid solution 

 of zinc chloride. 



CARUBIN OR SECALANE. 



Carubin J is the name given to a substance occurring in 

 the seeds of Ceratonia siliqua, and in various cereals such as rye 

 and barley. In its characters it closely resembles mannan, 

 and by some authors is regarded as identical with it ; when 

 dry, it is a spongy friable substance which swells upon the 

 addition of water. It is soluble in cold water and is optically 

 inactive. Its sugar is fermentable and non-crystalline. 



XYLAN. 



This substance may be obtained by extracting sawdust 

 from the wood of deciduous trees with dilute caustic soda after 

 preliminary extraction of the sawdust successively with 

 organic solvents, water, ammonia, and finally washing with 

 water. The yield of xylan obtainable from birch wood is, 

 according to Schorger, 197 per cent, but the amount obtained 



* Paton, Nanji, and Ling : " Biochem. Journ.," 1924, 18, 451. 



t Hashitani : " J. Inst. Brew.," 1927, 33. 347- 



jEffront : " Compt. rend.." 1897, 124, 200, and 125, 116 and 309. 



