32 THE CHEMISTRY OF CATTLE FEEDING 



is considered probable that that portion of the crude fibre 

 which is actually digested by the animals has the same 

 nutritive value as the so-called soluble carbohydrates. 



Dextrine. Dextrine is obtained as a colourless glassy 

 mass, or as a white amorphous powder, when perfectly dry. 

 It is readily soluble in water, but cannot be crystallised. The 

 solutions are colourless, tasteless and odourless, and are 

 optically active, [a] D = -f- 200 approximately. Dextrine is 

 insoluble in alcohol and is, therefore, precipitated from aqueous 

 solutions by this reagent. It gives no coloration with iodine 

 and does not reduce 1 Fehling's solution. 



The elementary composition of the substance corresponds 

 to the simplest formula, C6H 10 O 5 . It is said to yield a 

 dinitrate, C 6 H 8 O 3 (NO 3 )2, and other esters. On hydrolytic 

 treatment it yields maltose, which is further rapidly resolved 

 into dextrose. 



2C 6 H 10 5 + H 2 -> C 12 H 22 U 

 Ci 2 H 22 O n + H 2 -> 2 C 6 H 12 6 



It is not directly fermentable by yeast ; but in the presence 

 of diastase, which converts it into dextrose, it undergoes 

 alcoholic fermentation. 



As hydrolytic treatment does not generally tend to produce 

 condensation, but, on the contrary, to cause disintegration of 

 complex molecules, it is probable that the molecule of dextrine 

 contains at least 2(C 6 H 10 O 5 ). As a matter of fact the formula 

 is often written as C 12 H 20 O 10 . The exact molecular weight, 

 however, is uncertain and the constitution is very obscure. 

 It may be regarded as an intermediate compound between 

 starch and maltose. At least three different modifications are 

 known, and there is evidence that others can exist. Some of 

 these have recently been obtained in crystalline form. 



There is some uncertainty regarding the occurrence of 

 dextrine in the sap of plants, but it is probably produced in 

 the process of germination of starchy seeds, and by the 

 mastication of starchy foods by animals. No doubt exists 



1 The commercial product always contains sugars which reduce 

 Fehling's solution. 



