306 Bacteriological Analyses 



Chapter XXXIV. 

 BACTERIOLOGICAL ANALYSES 



While it is obviously beyond the scope and purpose of this 

 volume to discuss in detail the technique of bacteriological analyses 

 and microscopic preparations of the milk products described herein, 

 it is deemed advisable to offer some suggestions that may serve for 

 guidance of those who are not familiar with bacterial fermentations 

 in condensed milk. 



Sampling.— Take samples of all products contained in open 

 receptacles, such as fluid milk, plain condensed bulk milk, barreled 

 sweetened condensed milk and milk powder, in sterile, cotton plugged 

 test tubes, or in small sterile glass-stoppered bottles, and keep them 

 in a cool place, preferably not above 35 degrees F. until ready to use. 

 Keep canned condensed milk sealed in the original package until 

 ready to use. If already open, invert a petri dish or a beaker over 

 the can to avoid contamination from the air. 



Dilution for Numerical Counts. — Make dilutions in 250 c.c. 

 glass-stoppered flasks. Before opening sealed cans, thoroughly 

 wipe off the entire top with a sterile piece of cheese cloth soaked 

 in a saturated solution of mercuric bichloride or a 5 per cent solution 

 of carbolic acid and flame the top of the can. Open evaporated 

 milk cans by punching a hole into its top, large enough to insert the 

 discharge end of a graduated pipette. Open sweetened condensed 

 milk cans with a sterile knife or a sterile can opener. 



In the case of fluid milk and evaporated milk, measure with a 

 sterile graduated pipette two cubic centimeters of the product and 

 198 cubic centimeters of sterile water into the 250 c.c. flask. In the 

 case of plain condensed bulk milk, sweetened condensed 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 98 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 is preferable. 



The above represents the first dilution. The flask should be 

 carefully shaken until a hemogeneous mixture is obtained and the 

 soluble portions have been completely dissolved. 



From this first dilution further dilutions are made in sterile 

 water in glass-stoppered flasks, according to requirements. The 



