212 THE MILK QUESTION 



tion should therefore not be countenanced by health au- 

 thorities. 



Pasteurization with holding devices, sometimes called 

 perfect pasteurization, is the method most in vogue, and, 

 when properly carried out, is entirely satisfactoiy. The 

 pasteurized milk must at once be cooled and filled into 

 sterilized bottles by machinery. Every possible precau- 

 tion must be exercised to prevent contamination after the 

 milk has been heated. 



The milk is first heated to the desired temperature and is 

 then held in bulk at this temperature for the required 

 length of time. With a good holding device there is not a 

 loophole for any harmful bacteria to escape destruction. 

 Two forms of holding devices are used by dairymen. 

 One is the Wilmer pattern, which consists of a circular disk 

 divided into segments. In each segment is a container to 

 hold the milk. The containers are filled in turn, and the 

 apparatus may be so timed that it requires just twenty, 

 thirty, or forty-five minutes during which the milk is held 

 in any particular segment. The other holding device is 

 known as the Park tanks. They consist simply of large 

 cylindrical tanks into which the heated milk is carefully 

 poured and held for a given length of time. Milk in a large 

 cylindrical tank will gradually cool, and theoretically the 

 cooler milk should remain on the bottom while the warmer 

 oncoming milk should stay on top. If this simple law of 

 physics were not disturbed by counter-currents, irregular- 

 ities in the temperature of the oncoming milk, and other 

 reasons, the Park tank could be used as a continuous hold- 

 ing device, but on account of the irregularities in the tem- 

 perature of the heated milk, cross-currents, etc., it is neces- 

 sary to have three or four such tanks, the milk flowing from 

 one to the other in succession in order to be sure that no 

 particle of the milk escapes before the proper time. 



In order to satisfy public health requirements, pasteur- 

 izers must be efficient in operation, permitting a definite 



