Ii8 



THE BACTERIAL CONTENT OF MILK 



The temperature of the barns was 55° F. The results were as 

 follows : — 



* The number of bacteria was obtained from development on agar in Petri 

 plates. The nutrient medium contained 2 per cent, peptone and 1-2 per cent, 

 agar, and was faintly alkaline to litmus. One set of plates was usually left four 

 days at 20° C. and one set forty hours at 37° C, and then twenty-four hours at 

 20° C. From 5 to 30 per cent, more colonies developed as a rule in the plates 

 kept at room temperature than in those kept for twenty-four hours at 37° C. 

 The milk was diluted as required with 100 or 10,000 parts of sterile water and 

 I c.c. of the diluted milk was added to 8 c.c. of melted nutrient agar. 



Park also examined milk taken during winter in well-ventilated, 

 fairly clean, but dusty barns. Visible dirt was cleaned off the hair 

 about the udder ; milkers' hands were wiped but not washed ; milk 

 pails and cans were clean, but the straining cloths were dusty. The 

 milk was cooled within two hours after milking to 45° F. Under 

 these conditions Professor Park found an average of 1 5,500 bacteria 

 per c.c. at the time of milking, 21,666 after twenty-four hours, and 

 76,000 after forty-eight hours. In a third series the conditions were 



