162 LABORATORY GUIDE IN BACTERIOLOGY 



SECTION II 



A STUDY OF GROUPS OF BACTERIA IN MILK 

 (Ayers and Johnson) 



1. Prepare plates from a sample of milk. 



2. Pick off all colonies from a suitable plate and 

 inoculate each colony in a tube of litmus milk. 



3. Incubate for 2 weeks at 37 C. 



4. Note all reactions and classify in groups as 

 follows: 



a) Acid-coagulating group. 



b) Acid-forming without coagulation. 



c) Inert group, i.e., no change in the milk. 

 <f) Alkali-forming group. 



e) Peptonizing group. 



This experiment should be made with raw milk and 

 the same milk pasteurized. The results should be 

 compared. 



