138 BACTERIOLOGICAL DIAGNOSIS. 
those which are described in the section on the blood. 
There will be slight differences, but not enough to lead 
to error if the examination of the colonies is supple- 
mented by an inspection of stained films. 
The pneumococcus, gonococcus, the fungus of actino- 
myces, and the tubercle bacillus will not grow on these 
plates; and the bacillus of glanders will grow feebly, if 
at all. 
In a day or two longer the plates will, in some cases, 
be found to have undergone a decided change. If 
liquefying organisms are present the colonies will soon 
become depressed below the general surface of the 
medium and will be surrounded by haloes which 
consist of liquefied gelatin. This will happen with the 
staphylococci and the bacillus pyocyaneus; not with 
the streptococci, the typhoid bacillus, nor with the 
bacillus coli. lee 
The bacillus of blue pus can readily be distinguished 
from the staphylococci by its morphological appearance 
(it is a slender rod) and by the fact that the gelatin 
round the colony is coloured blue or bluish-green, the 
growth itself being nearly white. 
wesc 
INTERPRETATION OF RESULTs. 
The information which is obtained by a study of the 
bacteria in pus is of more scientific interest than of 
practical importance. It is the situation of the collec- 
tion of pus rather than the bacteria causing it which 
influences treatment and prognosis. A list of the more 
important results which are produced by the chief pyo- 
genic bacteria may be of interest. 
Staphylococci are the chief producers of localised 
suppuration in the skin—such, for instance, as that 
