4 CONSTITUENTS OF MILK 



a solution containing 10 grams per 100 c.cms. is 1.3461 and of a 



5 per cent solution 1.3395. 



Lactose is not fermented by ordinary yeast (Saccharo- 

 mycetes cerevicige) and is not affected by the ordinary enzymes. 

 The enzyme lactase, which is capable of hydrolysing lactose 

 into dextrose and galactose, is found as an endo enzyme in 

 Torula kefyr and T. tyrcola and also as an exo enzyme in 

 Kefyr grains. 



Lactose Dextrose Galactose 



Lactase is also widely distributed in the animal kingdom, 

 being present in the mucous membrane of the stomachs of 

 infants and also in the expressed juices of muscle, liver, lungs, 

 and pancreas. 



The action of acids generally is similar to that of lactase, 

 though the mineral acids are much more effective than those 

 of the organic series. Dextrose and galactose, according to 

 Fischer, have the following constitutional formulae: 



COH COH 



I I 



H C OH H C OH 



I I 



HO C H HO C H 



H C OH HO C H 



OH H C OH 



! I 



CH 2 OH CH 2 OH 



Dextrose Galactose 



These formulae show both sugars to be isomeric aldoses of 

 the monose type. Their specific rotatory powers [a] D are 



