204 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



venting milk from spoiling, and the process was adopted 

 by some dealers for this purpose, being used secretly by 

 many of them. Naturally, this brought the process into 

 disrepute. Sanitarians and public health authorities were 

 also disposed to discourage its use because of the ineffi- 

 ciency of the early apparatus and the lack of exact in- 

 formation regarding the effect of the process upon the 

 milk and the pathogenic organisms which may be con- 

 tained in it. With the acquirement of further informa- 

 tion on the latter phase of the subject and improvement 

 of the apparatus, sanitarians and public health officials 

 came to regard the pasteurization of milk, when prop- 

 erly carried out, as a legitimate and useful process and 

 by 1910 the pendulum had swung so far in the other 

 direction that many of them were advocating the pas- 

 teurization of all milk. 



PRINCIPLES OF PASTEURIZATION 



To obtain a correct conception of the hygienic value 

 of pasteurization, it is necessary to consider the effect of 

 different degrees of heat and periods of exposure upon 

 the pathogenic organisms which may be present in the 

 milk, upon the common milk bacteria, upon the toxins 

 and decomposition products resulting from bacterial 

 growth, upon the nutritive properties of the milk, and 

 upon the ferments or enzymes. Commercially, the effect 

 upon the taste and the separation of the cream is also 

 of importance. 



1. Effect of Heat on Pathogenic Organisms. The 

 disease-producing bacteria which occur most frequently 

 in milk are streptococci, the bacilli of tuberculosis, ty- 

 phoid fever and diphtheria, and the pyogenic staphylo- 

 cocci. The infectious agent of scarlet fever, which is 



