BACILLUS COLI 83 
EXERCISE XXXI 
BACILLUS COLI 
125. Of the bacteria normally present on the mucous mem- 
branes of the animal body the colon group is, on account of 
its close morphological relationship to the bacilli of typhoid 
fever and B. suipestifer, of more than ordinary interest. There 
are varieties of this organism which approximate very closely 
in their biochemic properties as well as in their morphology 
to the typhoid bacilli and also to B. suzpestifer. It is impor- 
tant that this existing yariation be recognized and that the 
list of properties which characterize B. co/i should be clearly 
determined. The differentiation of the colon and typhoid 
bacilli as they exist in nature is one of the difficult prob- 
lems in practical bacteriological work. This is especially true 
in water analysis. Many special media have been recom- 
mended to differentiate these organisms. The culture assigned 
approaches very closely to the typical species. 
126. Work for this exercise. Describe the appearance of 
each of the cultures made in Exercise XXX. 
Examine the bacteria in a hanging-drop preparation from 
the bouillon and glucose bouillon cultures. 
Make and stain with carbol fuchsin a cover-glass preparation 
from .the agar culture. Measure a few of the bacilli and 
record their size in the notes. 
Note especially the quantity of gas formed in each of the 
fermentation tubes. These cultures should be kept until the 
next exercise, when they should be examined again. If the gas 
formation is then completed, determine the quantity in each 
tube and the ratio of CO, to H. 
Make 2 gelatin plates from the bouillon culture. In mak- 
ing these plates use a tube of sterilized distilled water for the 
first dilution. a \ 
