GENERAL BACTERIOLOGY 89 



able circumstances produce disagreeable odors or 

 tastes), and such pathogens as the bacillus of tuber- 

 culosis (which may be derived from the cow, or may be 

 an accidental contamination), the typhoid bacillus, 

 the bacillus of "smnmer complaint" in children (pos- 

 sibly identical with the bacillus of epidemic dysentery), 

 the germs of cholera, diphtheria, and scarlet fever. 

 All these, except B. tuberculosis, flourish in milk at its 

 ordinary temperature. 



None of the methods employed in steriUzing milk 

 render it sterile in the bacteriological sense of the word, 

 but by means commonly employed most of the non- 

 sporing pathogenic bacteria are destroyed, along with a 

 large number of saprophytes, thus rendering milk 

 comparatively safe and less subject to ordinary fer- 

 mentative changes. 



I. Sterilization at 100° C, for 30 minutes. — Such 

 milk, if chilled and kept at a low temperature, will 

 remain unchanged 'for more than a week, but, by 

 heating, certain alterations have been produced in 

 taste and appearance. 



2. Pasteurizing milk. — ^The changes occurring in 

 milk, as above mentioned, begin at about 80° C. Pas- 

 teurization at a low temperature is accomplished by 

 raising the temperature to 60-65° C. for a period of 20 

 minutes. This has been shown to be sufficient to kill 

 the germs of tuberculosis, typhoid fever, cholera, 

 diphtheria, and pyogenic cocci. Spores are not killed. 

 As shown by Theobald Smith, tubercle bacilli, when 

 suspended in distilled water, physiological salt solution, 

 broth, and milk, are destroyed at 60° C. in 15-20 min- 



