CHAPTER XLVIL 



THE BACTERIOLOGY AND THE BACTERIOLOGIC EXAMINATION OF 

 MILK (CONTINUED) QUANTITATIVE ESTIMATION OF BACTERIA 

 IN MILK INTERPRETATION OF THE RESULTS OF BAC- 

 TERIAL COUNTS IN MILK DETERMINATION OF THE 

 ACIDITY OF MILK CERTIFIED MILK PASTEURIZA- 

 TION OF MILK ITS ADVANTAGES AND 

 DISADVANTAGES STORCH'S TEST. 



QUANTITATIVE ESTIMATION OF BACTERIA IN MILK. 



THE investigations of von Freudenreich, Henderson, and others 

 have shown that the milk ducts in the udder of perfectly healthy cows 

 contain numerous bacteria. Sedgwick and Batchelder, MacConkey, 

 Burr, von Freudenreich, Lux, and others have found the bacteria 

 contents of milk freshly drawn under all possible aseptic precautions, 

 and after the removal of the foremilk 1 and an additional liberal 

 amount of regular milk to be from 250 to 1500 per cubic centimeter. 

 But these figures form no basis for practical deductions when a 

 large amount of milk is collected in one pail. Russell found that the 

 mixed milk from a good herd, collected with care and cleanliness, 

 examined immediately after milking, showed from 5000 to 20,000 

 bacteria per cubic centimeter. After milk has been collected the 

 number of bacteria apparently decreases for a number of hours. 

 This is attributed to the germicidal property of milk. This question 

 has recently been re-investigated by Rosenau and McCoy, who come 

 to the following conclusions: 



"Judged by the number of colonies that develop upon agar plates, 

 the bacteria in milk first diminish, then increase in numbers. This 

 so-called germicidal property of milk occurs only in fresh, raw fluid. 

 For the most part our work plainly shows that no actual reduction 

 in the number of bacteria occurs. However, when compared with 

 the controls, a restraining action is evident. The phenomenon, 

 therefore, appears to resemble that of a weak antiseptic rather than 

 that of a true germicide. When milk is kept warm (37 C.) the 

 decrease is pronounced within the first eight or ten hours. After this 

 time the milk has entirely lost its restraining action. When the milk 

 is kept cool (15 C.) the decrease is less marked, but more prolonged. 

 The decrease in the number of bacteria is largely apparent, being due, 



1 L. Schulz found in various specimens of foremilk obtained from healthy udders, after 

 thorough external disinfection, from 50,000 to 79,000 germs per cubic centimeter. 



