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- 



