MILK 89 



(e) If collected at the byre, the number of cows from which 

 obtained should be given, and whether the milk has been strained 

 or not, and if so the strainer used. 



(/) If from individual cows, particulars of the quarter or 

 quarters from which obtained, and if fore, middle, or end milk. 



It is useful to take and record the temperature of the milk. 



Dilution of the Sample. 



In the bacteriological examination of milk the proper dilution 

 of the sample is of the utmost importance if accuracy is to be 

 obtained. It is important that the milk should be thoroughly 

 well shaken before dilution, and that the dilutions should be 

 well mixed. 



The following is the most convenient method of dilution. 

 A large number of glass-stoppered bottles of about 120 c.c. 

 capacity are used, each containing 90 c.c. of sterile tap-water 

 (Fig. 9). Sterile one-mark loc.c. pipettes are conveniently used 

 to add the milk, and these should be made short for convenience 

 of sterilization. After thorough shaking 10 c.c. of the milk is 

 removed and added to a 90 c.c. dilution bottle (Dilution A). 

 After well mixing 10 c.c. Dilution A is added to a second 

 90 c.c. bottle (Dilution B). In the same way Dilution C is 

 made from B and Dilution D from C. Each dilution, of course, 

 represents one-tenth dilution of the one immediately above it in 

 series. 



Small i c.c. pipettes graduated in tenths of a c.c. are used to 

 add fractions of the different dilutions to the requisite media. 



Dilution flasks or bottles containing 99 c.c. or 9 c.c. are often 

 used, and are recommended by the American Committee on 

 Standard Methods of Bacterial Milk Analysis 1 , but the writer is 

 of opinion that the addition of only I c.c. of milk for the primary 

 dilutions is unreliable and leads to error. By adding as much as 

 10 c.c. errors of measurement are reduced to a minimum, while 

 the use of glass-stoppered bottles enables the dilutions to be very 

 thoroughly mixed. 



1 American Jonrn. of Public Hygiene, 1910, XX, p. 315. 



