THE CARBOHYDBATES AND FATS 13 



sugar cane, beetroot, mallow, and sugar maple. It is a substance of 

 great importance as a food. After abundant ingestion of cane sugar 

 traces may appear in the urine, but the greater part undergoes 

 inversion in the alimentary canal. 



Pure cane sugar is crystalline and dextro-rotatorj-. It holds 

 cupric. hydrate in solution in an alkaline liquid — that is; with 

 Trommer's test it gives a blue solution. But no reduction occurs on 

 boiling. After inversion it is strongly reducing. 



Inversion may be brought about readily by boiling with dilute 



mineral acids, or by means of an inverting ferment, such as that 



occmTing in the succus entericus or intestinal juice. It then takes 



up water and is split into equal parts of dextrose and levulose (see 



p. 12). 



C12H22O1, + H2O = C6H12O6 +Cr,H,206 

 [cane sugar] [dextrose] [levulose] 



With yeast, cane sugar is first inverted by means of a special 

 soluble ferment produced by the yeast cells, and then there is an 

 alcohohc fermentation of the glucoses so formed. 



Lactose, or milk sugar, occurs in milk. It has also been described 

 as occurring in the urine of women in the early days of lactation or 

 after weaning. 



It crystallises in rhombic prisms (see fig. 3). It is much less 

 soluble in water than cane sugar or dextrose, 

 and has only a slightly sweet taste. It is 

 insoluble in alcohol and ether ; aqueous 

 solutions are dextro'-rotatory. 



Solutions of lactose give Trommer's 

 test, but when the reducing power is tested 

 quantitatively by Fehling's solution it is 

 found to be a less powerful reducing agent 



than dextrose. If it required seven parts fig. 3.— MUk-sugar crystals, 

 of a solution of dextrose to reduce a given 



quantity of Fehling's solution, it would require ten parts of a solution 

 of lactose of the same strength to reduce the same quantity of 

 Fehling's solution. 



Lactose, like cane sugar, can be hydrolysed by the same agencies 

 as those already enumerated in connection with cane sugar. The 

 glucoses formed are dextrose and galactose. 



C,2H220n + H2O = G,B.,,0, + C,H,20„ 



[lactose] [dextrose] [galactose] 



With yeast it is first inverted, and then alcohol is formed. This, 

 however, occui's slowlv. 



