THE CARBOHYDRATES 



H 



lactose 



HO H HO HO 



OHC - C - C - C - C - CH 2 glucose rest 

 H OH H H 



A very large number of glucosides occur as plant product/ Among these we n 

 mention amygdalm, salicm, phloridzin, indican, &c. 



THE DISACCHARIDES 



The disaccharides are formed by the union of two molecules of mono- 

 saccharides with the elimination of one molecule of water, and can be re- 

 garded, according to the manner in which the molecules are combined, as 

 glucosides, galactosides, &c. On hydrolysis, e.g. on heating with acids, they 

 take up one molecule of water and are split up into the corresponding mono- 

 saccharides. Thus, cane sugar gives equal parts of glucose and fructose, 

 maltose gives equal parts of glucose and glucose, while milk sugar or lactose 

 gives equal parts of glucose and galactose. 



CANE SUGAR, sometimes known as saccharose, is widely distributed 

 throughout the vegetable kingdom, and forms an important article of diet. 

 It has no reducing power on Fehling's solution. It is strongly dextro-rota- 

 tory and has a specific rotatory power of + 66-5. On hydrolysis it is 

 converted into equal molecules of glucose and fructose. Owing to the fact 

 that fructose rotates polarised light more strongly to the left than glucose 

 does to the right, the mixture of the two monosaccharides so obtained is 

 Isevo- rotatory. On this account the change from free cane sugar to the 

 mixture of monosaccharides is known as inversion, and the mixture is often 

 spoken of as ' invert sugar.' The term ' inversion ' has since been loosely 

 applied to the process of hydrolysis itself, so that we often speak of the 

 inversion of maltose or of lactose, meaning thereby the hydrolysis of these 

 sugars with the production of their constituent monosaccharides. With 

 yeast, cane sugar first undergoes inversion by a special ferment present in the 

 yeast (invertase), and the mixture of fructose and glucose is then fermented. 



MALTOSE is formed during the hydrolysis of starch by acids or by 

 digestive ferments, and is also the chief sugar in germinating barley or malt. 

 It is strongly dextro-rotatory, ferments easily with yeast, and reduces 

 Fehling's solution ; its reducing power is about 70 per cent, of that of 

 glucose. With phenyl hydrazine it gives phenyl maltosazone, which forms 

 definite yellow crystals with a melting-point of 206 C. 



MILK SUGAR or LACTOSE is found only as a constituent of 

 It forms colourless rod-like crystals, which are much less soluble in v 

 than are the two other disaccharides. On account of this solubilu 

 less sweet than either cane sugar or maltose. It is dextro-rotatory 



