142 ESSENTIALS OF BACTERIOLOGY 



A serum in a dilution of i : 100 causing complete clumping 

 in half an hour is undoubtedly typhoid. 



The culture must be kept in a vigorous condition by fre- 

 quent subplanting, and must be tested occasionally with 

 normal serum. Cultures kept in an incubator for a long time 

 tend to agglutinate spontaneously. 



Macroscopic Agglutination Test. Where laboratory facili- 

 ties are not available, the sedimentation test is practical. 

 It consists in adding the diluted blood or serum to be tested 

 to a suspension of dead typhoid bacilli in salt solution. If 

 the reaction is positive, a flocculent precipitate forms which 

 consists of masses of agglutinated bacilli. A control tube con- 

 taining normal serum and the suspension should remain 

 opaque and show no flocculi. 



Differentiation Between Colon and Typhoid. The 

 colon bacillus and the typhoid bacillus resemble each other 

 so closely that much attention has been paid to methods of 

 differentiation. 



Points of Resemblance Between Bacillus Typhi and Bacillus 

 Coli Communis. First, microscopic appearance; second, agar 

 and gelatin cultures; third, sometimes growth on potato the 

 same; fourth, staining peculiarities; fifth, resistance to phenol. 



Points of Difference: 



Colon Bacillus. Typhoid Bacillus. 



Bile media, gas. None. 



Less motile. Actively motile. 



Gelatin colonies develop Develop slowly. 



more rapidly. 



Produces gas on dextrose or Does not. 



lactose media. 



Coagulates milk. Does not. 



Produces indol. Does not. 



Growth on potato visible. Invisible. 



Changes neutral red to Does not reduce neutral red. 



yellow. 



Endo-fuchsin red. Not. 



