3ACTERTOLOGICAL ANALYSES 375 
milk and milk powder, use:tared flasks holding about 150 cubic 
centimeters, weigh into them two grams of the product and add 
enough sterile water at a temperature of YS degrees F. to make 
up 100 cubic centimeters. Use a sterile spoon or spatula to 
transfer the product to this flask. A wide-mouth flask ts 
preferable. 
The above represents the frst dilution. The flask should be 
carefully shaken until a homogeneous mixture is obtained and 
the soluble portions have been completely dissolved. 
From this dilution further dilutions are made in sterile 
water in glass-stoppered flasks, according to requirements. The 
dilutions should be sufficient to limit the number of colonies on 
the plates to about 50 to 100 per plate. Whole milk, as it arrives 
at the factory, usually shows from 100,000 to 1,000,000 bacteria 
per ce. Evaporated milk should be practically sterile unless the 
can shows signs of fermentation in which case the number of 
bacteria present will depend on the age of the sample can; 
dilutions as high as 1:1,000,0CO are recommended in such cases. 
Plain condensed bull milk when fresh contains from about 
1,000 to 100,000 bacteria per ¢.c., when several days old and in 
the absence of refrigeration, its germ content is often much 
ereater. Sweetened condensed milk averages from about 500 to 
500,000 bacteria per c.c. 
Plating.—Ior plating the following media are recommended : 
Media for Total Counts and also for acidifiers 
4 grams beef extract 
10 grams peptone 
30 grams lactose 
4 erams sodium chloride 
12 grams thread agar 
1000 c.c. distilled water. 
Acidity 0.1 per cent. 
For acidifiers add 1 c.c. of sterile litmus solution to each 
plate before pouring the agar. 
Media for Liquefiers 
4 gerams beef extract 
10 grams peptone 
