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The Cornell Reading-Courses 



experiments that if the milk is cooled and held at a temperature of 50° 

 or lov/er, there will be very little increase in the number of bacteria in 

 twenty- four or thirty-six hours. The lower the temperature, the more 

 completely the bacteria will be held in check. The effect of temperature 

 on the growth of bacteria and on the keeping quality of milk may be 

 seen in the following table : 



Effect of Different Temperatures on the Development of 



Bacteria in Milk 



Temperature maintained for 12 hours 



40° 



45. 

 50.. 



55- • 

 60.. 



70. 

 80. 



Bacteria per cc. 



at end of 12 



hours 



4,000 



9,000 



I 8 , 000 



38,000 



453.000 



8 , 800 , 000 



55,300,000 



Hours to curdling 

 at 70° 



75 

 75 

 72 



49 

 43 

 32 

 28 



The above results were obtained by dividing a quantity of milk itito 

 seven parts and holding the samples at the temperatures indicated for' 

 twelve hours. The number of bacteria in each was then determined 

 and all the samples were placed at a uniform temperature of 70° until 

 they curdled. The difference in bacteria content and keeping quality, 

 therefore, was due to the difference in temperature for the twelve-hour 

 period. If the samples had been held continuously at the different tem- 

 peratures, the effect on the bacteria and on the keeping quality would 

 have been still greater. The practical point in this experiment is the 

 fact that the samples held at 50° or below kept remarkably well, while 

 those held at the higher temperatures spoiled more readily. This in- 

 dicates that if milk is to be kept in good condition it should be held at 

 a temperature not much above 50°. 



It is not a difficult thing to keep milk in excellent condition for 

 a sufficient length of time to allow its use in the household, if the 

 necessary precautions are taken. The first essential is for the housewife 

 to procure milk that has been produced and handled under reasonably 

 clean conditions. It can then be kept in good condition if it is not exposed 

 to foreign odors and is held at the temperatures found in a good ice chest 

 or refrigerator. 



