Preservation of Milk. 49 



cheapest and most efficient. The use of preservatives 

 is prohibited by law in every state and their use, if de- 

 tected, punishable by fine. Their use is prohibited 

 since these substances are looked upon as injurious to 

 human health. There is not much temptation for the 

 farmer to use them, the city dealer is more tempted, 

 since by their use he can carry over to the next day the 

 surplus milk and economize in the use of ice. One 

 ounce of formalin costing two cents added to 1,000 

 pounds of milk will cause it to keep for twenty-four to 

 forty-eight hours longer than it otherwise would. 



Bicarbonate of soda does not prevent the growth of 

 bacteria, but does, by neutralizing the acid formed, de- 

 lay the time when the milk begins to taste sour. The 

 remainder of the substances mentioned act by retard- 

 ing the growth of the bacteria. 



Pasteurization of milk. As has been stated, the bac- 

 teria, especially the vegetative forms, are easily killed 

 by heat. The temporary preservation of food by heat- 

 ing is a common custom. It is constantly made use of 

 by the housewife in order to save some food that she 

 knows will be spoiled in a short time if it is not so- 

 treated. 



When this process is applied to milk in the house- 

 hold or on a commercial scale it is known as pasteuriza- 

 tion. It received its name from the originator of the 

 method, Pasteur, the great French bacteriologist, who 

 first used it for the preservation of the wines of his 

 native district in France. It was later used by brew- 

 ers in order to prevent the formation of sediment in 

 beers. Today much of the bottled beer is pasteurized. 

 The process was later adopted by the dairy industry, 

 and here has been widely used. The process is carried 



