PRESERVATION OF MILK 379 



In Pig. 35 is shown an illustration of a good type of 

 pasteuriser of the retainer pattern. 



The thermal death-points of the different bacteria likely 

 to be present in milk are considered in Chapter IV. The 

 tubercle bacillus is the most important organism to kill, and 



Fig. 35. — "Retainer" type of Pasteuriser. 



being more resistant than the others, the temperature 

 and time exposure which will kill this bacillus may be taken 

 as the standards for practical purposes. From the experiments 

 recorded in Chapter IV. it would seem that an exposure to 

 71° C. (160° F.) for one minute or to 60° C. (140° F.) for 

 20 minutes is sufficient. Since, however, as pointed out in 



