PASTEURIZATION OF MILK. 163 



water; if they do not break immediately in such a case 

 they will become brittle and readily break in the next 

 boiling. Milk residues in the bottles should not be saved. 

 The cleaning of the bottles is best effected as soon as the 

 milk has been consumed. 



Ardent adherents of Soxhlet's method claim that milk 

 treated in this way will keep for three to four days, and 

 advise that large quantities of milk be sterilized at once. 

 This is doubtless an exaggeration. One of the best points 

 in the method is in my opinion the fact that small quanti- 

 ties of milk may be easily and cheaply treated. If such 

 incompletely sterilized milk is saved for a longer time than, 

 e.g., twenty-four hours, risks are doubtless taken. If living 

 bacteria are found in milk they will necessarily soon make 

 their presence known if it is kept longer, and not in a 

 cool place. 



Milk treated according to Soxhlet's method seldom 

 becomes absolutely sterile. I have made numerous ex- 

 periments on this point and have kept milk carefully 

 prepared in a Soxhlet apparatus at a temperature of 90 F. 

 (32 0.) in an incubator; I have practically every time 

 within forty- eight hours been able to verify in it a large 

 number of Bacillus-subtilis forms and other bacteria. 

 Soxhlet warns against sterilizing such large quantities at 

 one time that the milk has to be kept long before being used. 

 He holds that lactic acid is almost exclusively formed in 

 unboiled milk kept at 95 F. (35 C.); butyric acid formed 

 at the same time does not make up even 4 per cent of the 

 total acidity. Large quantities of butyric acid are, on the 

 other hand, formed in samples of partially sterilized milk 

 at least 15 per cent, on an average 30 per cent, and often 

 more than 50 per cent of the total acidity. This butyric 



