210 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
power of milk. It was therefore naturally supposed that 
bacteria would develop more rapidly in pasteurized than 
in raw milk. Rickards compared the average increase 
of bacteria occurring in a number of samples of raw and 
pasteurized milk and found that bacteria multiplied four 
times faster in commercially pasteurized milk than in 
raw milk at ice-box temperature. Ayers and Johnson 
contend, however, that when the growth of bacteria in 
pasteurized milk is compared with the growth of bacteria 
in the same grade of raw milk the increase of bacteria 
is about the same in both kinds of milk. But Savage 
is of the opinion that organisms which gain access to 
milk after pasteurization will grow more rapidly than in 
raw milk if for no other reason than because the bac- 
terial content is much less and the conditions for growth 
therefore much more favorable. These facts illustrate 
the importance of promptly cooling pasteurized milk and 
keeping it cool, and also indicate the necessity of pre- 
venting the access of any bacteria, and especially patho- 
genic organisms, after pasteurization. 
3. Toxins and Decomposition Products. — The 
growth of bacteria in milk is attended by the produc- 
tion of toxins and also by the decomposition of some of 
the milk constituents. The extent to which these changes 
occur will depend upon the number of bacteria which 
gain access to the milk during the drawing of the milk 
and its subsequent handling, the age of the milk at the 
time of pasteurization, and the temperature at which it 
has been kept in the meantime. 
While the true or soluble toxins (exogenous, extra- 
cellular) are destroyed at comparatively low tempera- 
tures, the endotoxins (endogenous, intracellular) are 
quite resistant to heat. Most of them require a tempera- 
