BACILLUS COLI COMMUNIS. 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 Elsner medium the colon colonies appear 
earlier and become larger and moré 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- 
