MILK-SUGAR. 25 



Hueppe, Hueppe has shown that its development ceases below 

 temperatures of 10 C., is very feeble at 12 C., increases very 

 much above 15 C., and goes on briskly at temperatures between 

 35 C. and 42 C. When the temperature is raised above 42 C. 

 its development diminishes, until, at between 45'3 C. to 45'5 C., it 

 entirely ceases. Practical experience has shown that with regard 

 to other bacteria effecting lactic fermentation, rapid development 

 only begins at a temperature above 15 C. 15 C., therefore, may be 

 regarded as the temperature below which warm milk should be 

 cooled as quickly as possible if it is to be kept, and above which 

 cold milk should not be warmed if its keeping quality is not to be 

 impaired. The reason, therefore, why milk at 16 C. to 20 C. will 

 keep, even under the most favourable conditions, for only some 50 

 hours, and why it becomes necessary to have recourse to costly and 

 inconvenient preservative measures, is due almost entirely to the 

 milk-sugar present in the milk. In practice the only admissible 

 physical means for the prevention of premature souring in milk is 

 the cooling of the milk below 10 C., or heating it above 50 C. The 

 treatment of milk with chemicals (sodium carbonate, boracic acid, 

 salicylic acid, hydrogen peroxide, &c.) for effecting this purpose is 

 to be absolutely condemned. 



Milk-sugar (Iodine, lactose, C 12 H 22 O n . H 2 0) was first discovered 

 as a constituent of milk in 1619 by Bartoletti. It crystallizes in deep 

 rhombic prisms, of a white transparent colour, and contains 5 per cent of 

 water of crystallization. It is comparatively hard, and is insoluble in 

 absolute alcohol and ether. It is soluble in 2J parts of boiling water, and 

 6 parts of cold water. In concentrated solutions it presents a viscous 

 appearance, and exhibits a tendency to form supersaturated solutions. It 

 is only slightly sweet to the taste. Its specific gravity, compared with 

 water at 4 C., is 1'545, and its elementary composition is as follows: 



Carbon, 40'00 



Hydrogen, 6-11 



Oxygen, 48*89 



Water of crystallization. ... ... ... 5*00 



100-00 



Crystallized milk-sugar does not part with its water of crystallization 

 when heated to 100 C. On being heated for some time to a temperature 

 of from 100 to 130 C., it becomes slightly brown in parts, and begins to 

 decompose : a slight quantity of oxygen is absorbed, and a corresponding 



