94 Report of the Department of Bacteriology of the 



technique. 



The last 922 samples were obtained and handled in accord with 

 the following general outline: 



All samples were collected from the afternoon milkings and 

 those from the Station herd were taken from each cow on three 

 successive days. The cows from which the samples were taken 

 had been carefully groomed but no local disinfection of the udder 

 was attempted. The milking was done by hand, in the ordinary 

 way, directly into sterile test tubes. With the exception of a single 

 series, where the object was to test the condition of the milk at the 

 yarious stages of milking, the samples were from the close of the 

 milking. Care was exercised that the sample was the product of 

 a single stream of milk and that the sterile tube was opened for 

 the minimum time and was held in such a manner as to be exposed 

 to the minimum amount of contamination. 



The samples from the Station cows were taken to the laboratory 

 and the plating completed within an hour, those from other 

 sources within three hours. The medium used was as follows: 



Agar 15 grams. 



Peptone (Witte) 10 " 



Lactose, c.p 10 " 



Beef extract (Liebig) 5 " 



Water (dist.) to make a volume of 1000 cc. 



The reaction of this medium ordinarily was between 1.2 and 

 1.5 per ct. normal acid to phenolphthalein. Whenever it exceeded 

 the higher figure it was reduced by the addition of XaOH. This 

 medium was chosen to permit incubation both at 20° C. and 37° C. 



In plating, one cubic centimeter of milk was divided between 

 two petri dishes and approximately 8 cc. of the agar was added 

 to each plate. The sum of the colonies developing on these two 

 plates was taken as the germ content of the milk. The plates 

 were held at room temperature (20-23°( 1 .) for five days and 

 the first count made. They were then placed at 37 °C. for two 

 additional days and counted again. All counts were made under 

 a lens magnifying four diameters. 



