1 76 MILK AND THE PUBLIC HEALTH 



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

 Sterile one-mark 10 c.c. pipettes are conveniently used to add 

 the milk to the dilution bottles, and these should be made 

 short for convenience of sterilisation. After thorough shaking 

 10 c.c. of the milk is removed and added to a 90 c.c. dilution 

 bottle (Dilution A). (See Fig. 7.) 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 a tenfold 

 dilution of the one immediately above it in series. 



Small 1 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 Com- 

 mittee on Standard Methods of Bacterial Milk Analysis, 1 but 

 the writer is of opinion that the addition of only 1 c.c. 

 of rnilk 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 Journ. of Public Hygiene, 1910, xx. p. 315. 



