372 MILK AND THE PUBLIC HEALTH chap. 



I. Eefkigeration 



The scientific facts which bear upon this question have 

 been discussed in Chapter IV. In that chapter it was shown 

 that at temperatures ranging from freezing to blood-heat the 

 higher the temperature of the milk the more rapid the 

 multiplication of the contained bacteria. It may be concluded 

 from the figures there given that if samples are kept at 0° C. 

 for reasonable periods (i.e. not more than forty-eight hours) no 

 increase in the number of bacteria takes place. Even if 

 kept at 10° C. no marked increase takes place within twenty- 

 four hours. Eefrigeration can therefore be made efficient. 



There is further no evidence that any prejudicial effects 

 upon the digestive properties of the milk result by refrigeration. 



Cooling the milk even to 0° C. does not diminish any 

 bacterial harmfulness it may possess ; it will not, for example, 

 injure pathogenic bacteria ; but it prevents the increase of 

 toxic properties by preventing the multiplication of bacteria 

 already present and the production of their toxic products. 

 It is obvious, therefore, that the place of cooling should be at 

 the farm and not when it reaches the purveyor. The latter 

 may have to cool the milk for his own protection, but he is 

 merely preserving what may already be a damaged product 

 from deteriorating still further. 



The cost will depend upon the facilities for obtaining ice, 

 the degree of cooling required, etc. Types of milk coolers are 

 described on pages 288 and 289. 



As regards the cooling of milk as a method of artificial 

 preservation, summing up the matter, it may be said that it is 

 efficient and harmless and by far the best available method. 

 The degree of efficiency attained will depend upon the tem- 

 perature adopted. For practical purposes 10° C. is a convenient 

 temperature and one sufficiently efficient. The extent to which 

 it can be used need only be governed by the question of cost 

 and its influence upon the price of the vended article. 



II. Sterilisation 



The term " sterilised milk " has two meanings, the 

 scientific and the meaning of the trade. To the bacteriologist 

 sterilised milk means milk which is sterile, that is, free from 



