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 
