BACILLUS CO LI COM MUNIS. 455 



color of the colonies of the colon bacillus is pink and 

 the surrounding medium becomes red; while the colonies 

 of the typhoid bacillus are blue, and there is little or no 

 reddening of the surrounding medium. 



7. The colon bacillus possesses the property of pro- 

 ducing indol in cultures of bouillon or peptone; the 

 typhoid bacillus in these solutions does not produce 

 indol, except in a few rare exceptions. 



8. The colon bacillus rarely produces thread out- 

 growths in the Hiss plate medium. The typhoid bacil- 

 lus produces thread outgrowths and smaller colonies in 

 this medium. In the Hiss tube medium the colon 

 bacillus produces either a growth limited to the area 

 inoculated or a diffuse growth streaked with clear lines 

 and spaces. The typhoid bacillus produces a diffuse 

 growth evenly clouding the entire medium. 



9. On the Capaldi medium the colon colonies are 

 more granular and darker than those of the typhoid 

 bacilli. 



10. On the Eisner medium the colon colonies appear 

 earlier and become larger and more opaque than the 

 average typhoid colonies. 



11. Finally, we have the test of placing the bacilli 

 in animals and in the hanging drop, together with the 

 serum of animals immunized to either the colon or the 

 typhoid bacillus. 



None of these tests alone can be depended upon for 

 making a differential diagnosis of the colon bacillus 

 from the typhoid bacillus or other similar bacilli. 



Unfortunately in most, at least, of these characters 

 certain degrees of variation may often be observed in 

 different cultures of the typhoid and colon bacillus 

 which may lead to confusion. For instance, the mor- 



