CONTROL OF THE MILK SUPPLY 



229 



Low temperatures, it is true, do not easily destroy life, but they 

 have a most beneficial effect upon the keeping quality of milk. It 

 has been suggested that at the outset of the process of cooling, 

 currents of air, inimical to bacteria, are started in the milk. If, 

 however, the temperature be lowered sufficiently, the contained 

 bacteria become inactive and torpid, and eventually are unable to 

 multiply or produce their characteristic fermentations. At about 

 50 F. (10 C.) the activity ceases, and at temperatures of 45 F. 

 (7 C.) and 39 F. (4 C.) organisms are practically deprived of their 

 injurious powers. If it happens that the milk is to be conveyed 

 long distances, then even a lower temperature is desirable. The 

 most important point with regard to the cooling of milk is that it 

 should take place immediately. Various kinds of apparatus are 



FIG. 23.-" Ulax " Filter. 



effective in accomplishing this. Perhaps those best known are 

 Lawrence's cooler and Pfeiffer's cooler, the advantage of the latter 

 being that during the process the milk is not exposed to the air. 

 It must not be forgotten that cooling processes are not sterilising 

 processes. They do not necessarily kill bacteria; they only 

 inhibit activity, and under favourable circumstances torpid pathogenic 

 bacteria may again acquire their injurious faculties. Hence, during 

 the cooling of milk greater care must be taken to prevent aerial 

 contamination than is necessary during the process of sterilising 

 milk. No cooling whatever should be attempted in the stable; 

 but, on the other hand, there should be no delay. Climate makes 

 little or no difference to the practical desirability of cooling milk, 

 yet it is obvious that less cooling will be required in the cold season. 

 The final treatment of milk has in practice comprised the addition 

 of preservatives, filtration, and sterilisation. 



