PRESERVATION OF MIJ.K 211 



teria; so that through the agency of the soap and the 

 boiling water the milk receptacles are pretty thoroughly 

 cleaned. Glass vessels are more satisfactory than others, 

 since it is much easier to tell whether they are clean. Glass, 

 however, is easily broken in hot water, and care must be 

 taken in the cleaning. Drying the milk vessels after wash- 

 ing is a process in which perhaps more care is necessary 

 than in the actual washing. If a well cleaned milk pail or 

 bottle is closed tightly immediately after washing and 

 wiping (or even inverted unclosed on a flat surface in such 

 a way as to exclude the air) enough moisture remains in 

 it to permit the growth of bacteria. Such a vessel after a 

 few hours is in a more filthy condition than before wash- 

 ing; if any one questions the statement, let him leave a 

 freshly washed nailk vessel tightly closed half a day, then 

 open it and smeU the interior ! A milk vessel after scald- 

 ing should be thoroughly wiped, and then allowed to 

 stand right side up and open to the air until next 

 used. 



3. Temperature. The effect of temperature upon the 

 keeping of milk is more striking than its effect upon that 

 of any other food. Since milk may be frozen, it may be 

 kept in that condition for weeks, months, or even years 

 withdut change. Freezing has not, however, proved a prac- 

 tical method of preserving milk. But other means of cool- 

 ing are in constant use. Milk is frequently placed in a 

 cellar, since the temperature is lower there than in the rest 

 of the house. Another widely adopted plan, though not a 

 satisfactory one, is to lower the milk into a well, where, 

 since it is near the water, it is cooled. A more practical and 

 widely used device is the refrigerator, in which low tempera- 



