34<^ 



Constant Care Is Needed for Health unit vi 



Fig. 306 The milk bottles are filled when they are under the tanks and capped by 

 the machine holding the paper tubes. '\]l?at is the advantage of filling and capping 

 milk bottles by machine? (national dairy council) 



hour. This is far from the boihng point, 

 and the milk is not changed to a great 

 extent. The temperature is sufficient, 

 however, to kill the pathogenic bacteria 

 that may have entered by accident. Pas- 

 teurization also kills some of the other 

 bacteria which are found in huge num- 

 bers in even the cleanest milk. You can 

 see how plentiful bacteria are in milk by 

 placing a few drops on nutrient agar. 

 See Exercise 4. Many of the bacteria in 

 milk are of the kind that cause sourinr. 

 The moderate temperature of pasteuri- 

 zation does not kill them; it merely stops 

 their growth. Therefore, the milk should 

 be iced immediately after it has been 

 heated and should be kept cold, in re- 



cent years a simple test has been devised 

 to show whether milk has been heated 

 sufficiently to free it of pathogenic bac- 

 teria. Raw milk contains an enzyme 

 (phosphatase) which is easy to test for 

 and which is destroyed by the amount 

 of heat which should be applied during 

 pasteurization. If a sample of pasteurized 

 milk still shows the presence of this en- 

 zyme, it is clear that insufficient heat was 

 used in the pasteurization. 



In large cities, officers of the board of 

 health regularly inspect the pasteurizing 

 plants. Dairy fanns are also inspected to 

 make sure that all rules for the proper 

 keeping of cows and handling of milk 

 are obeyed. In spite of this inspection. 



