PATHOGENIC BACTERIA IN MILK 227 



All the white colonies should be investigated. One method 

 is to pick off and subcultivate in broth each white colony, 

 incubating at 37 C. until next day. All the broths are 

 then examined in hanging drop, and those which show actively 

 motile bacilli tested with antityphoid serum. A fairly powerful 

 serum should be used, and a dilution of not less than 1 per 

 cent employed. 



A quicker and often preferable method is to directly 

 test each of the white colonies with the antityphoid serum 

 by rubbing up a little of the colbny in a drop of 1 per 

 cent serum on a cover-glass. Only those which react are 

 subcultivated. All those which fail to show agglutination 

 are rejected, while those reacting are each subcultivated into 

 litmus milk, glucose litmus broth (in a double tube), and 

 lactose peptone solution (in a double tube). All the organisms 

 giving cultural characters in these media which accord with 

 those of B. typhosus are then fully worked out. The tests 

 should include accurate and extended agglutination tests with 

 highly dilute sera. 



Some such procedure as the above will rapidly decide 

 whether any typhoid bacilli have been isolated. 



The isolation of Spirillum cJiolerae and other pathogenic 

 bacteria may be carried out on the general lines set out in 

 text -books of bacteriology, and these should be consulted. 

 They are not sufficiently frequently met with in milk to 

 warrant a special description in this place. 



