74 PHYSIOLOGICAL CHEMISTRY 



Cane sugar does not reduce the usual carbohydrate reagents, 

 such as Fehling's or Benedict's solutions and it does not form an 

 osazone if treated with phenylhydrazine. This is due to its mo- 

 lecular structure. The aldehyde and ketone groups of its con- 

 stituents are no longer free. On long boiling with these reagents, 

 however, or after the action of an inverting enzyme on the cane 

 sugar, the solution will give positive reactions with the above re- 

 agents since the sugar is split into its constituent parts. The hy- 

 drolysis or splitting of cane sugar is called inversion because the 

 solution, originally dextrorotatory, is levorotatory after hydroly- 

 sis. This is due, of course, to the fact that the hydrolyzed solu- 

 tion contains equal quantities of glucose and fructose, the latter 

 of which rotates more strongly to the left than does glucose to 

 the right. The mixture is known as " invert sugar." A solu- 

 tion of cane sugar ferments readily with ordinary yeast, which 

 contains an enzyme invertase which will invert the cane sugar. 

 The resulting glucose and fructose are fermented by the zymase. 



Lactose. Lactose is found in the milk of all mammals, but 

 does not occur in plants. Cow's milk contains about 4% lac- 

 tose, human milk about 5% to 7%. It may occur in the urine of 

 women during pregnancy. Lactose is prepared from whey. 

 On concentration, lactose crystallizes out, and may be purified 



H 

 CH 2 OH C = 



I I 



CHOH CHOH 



I I 



CH 



C 



CHOH 



HOH O CHOH 



CHOH 



CH CH 



G-alactose Glucose 



Lactose 



