2l6 BACTERIA, YEASTS, AND MOLDS 



keep longer, and at the same time does not produce the 

 chemical changes which a higher temperature will. Pasteur- 

 ized milk at this temperature does not have the taste of 

 boiled milk and is as easily digested as raw milk. 



In an ordinary household it is almost impossible to find 

 any servant in the kitchen who can satisfactorily use a ther- 

 mometer, and even the housewife herself would hardly under- 

 take to heat milk at a temperature of 145° for half an hour. 



Fig. 68. Apparatus for home pasteurization of milk. The figure on 

 the right shows method of cooling the milk by running water. 



The only way it can be accomplished is by some device which 

 will bring about the result in a simpler way. The most con- 

 venient apparatus for this purpose is that shown in Fig. 68. 

 This consists of a series of bottles which readily fit into 

 cylinders placed in a larger vessel. This receptacle is filled 

 with boiling water, and the bottles, filled with milk, are placed 

 in the cylinders. The whole is set aside to cool. The milk 

 is warmed by the hot water surrounding it, and the water 

 is at the same time cooled by the milk. The size of the 

 vessel is so proportioned to the botdes that, when properly 

 used, the milk is heated to about the temperature desired 



