THE PASTEURIZATION OF MILK 



handled by them, the reader is warned that effi- 

 ciency tests are sometimes misleading. It should 

 be remembered that at least four factors enter into 

 the causes which produce the effects indicated. 



1st. The character of the apparatus itself. 



2nd. The carefulness with which the plant is 

 operated by those responsible for it. 



3rd. Whether the apparatus is thoroughly 

 cleaned and sterilized. 



4th. The character of the milk treated. 



It is, of course, understood by all those familiar 

 with bacteriological work that these are factors of 

 error in the results which can never be entirely 

 overcome. 



If apparatus is so constructed that the heating 

 and holding and cooling are true to their indicated 

 capabilities, then the results will be good if the 

 machine is properly operated and if it is clean. 

 These factors being reliable, the results can be 

 taken at their face value if the milk is of normal 

 quality and does not contain, we will say, certain 

 forms of bacterial life which are difficult to destroy. 



When results are good, it undoubtedly means 

 that both the apparatus and its operation are sat- 

 isfactory. If the results are bad, it is not always 

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