Preservation of Milk. 117 



such as certain of the putrefactive forms grow slowly; 

 the milk may, therefore, have no objectionable odor or 

 taste and yet be swarming with bacteria. In cities the 

 practice is followed of placing cream in cold-storage dur- 

 ing the cooler periods of summer in preparation for an 

 increased demand, during hot weather or on holidays. 

 It seems probable that poisoning from ice cream may, at 

 times, be due to the use of such cream. 



Preservation by the use of antiseptics. Many chem- 

 ical substances prevent the growth of bacteria when 

 added to food supplies; such substances thus used are 

 called preservatives. In the past some of these have 

 been used in milk to a great extent, but at present, on 

 account of stringent pure food laws, they are employed 

 only to a slight extent. There is a great temptation for 

 the small milk dealer in the city to employ them to pre- 

 serve the excess of milk from day to day, as through the 

 use of a few cents worth of some preparation, many dol- 

 lars worth of milk may be kept from spoiling until it 

 can be sold to the unsuspecting consumer. 



Formalin has been most widely used in milk because 

 it is a most efficient preservative ; it is cheap and cannot 

 be detected by the consumer, although it injures the 

 digestibility of the casein. One ounce will keep one 

 thousand pounds of milk sweet for twenty-four to forty- 

 eight hours. Borax, boric acid, and salicylic acid have 

 also been used, but these substances must be employed in 

 much larger quantities than formalin. Bicarbonate of 

 soda has sometimes been used although it is not a true 

 preservative. Its effect is based upon the neutralization 

 of the acid produced by bacterial growth. The treated 

 milk does not taste sour so quickly, and the curdling of 

 the milk is also delayed. 



