182 BACTERIOLOGICAL DIAGNOSIS. 
The colonies of the pmewmococcus are small flat white 
points which do not tend to fuse together. They are 
difficult to see when they are young, and in case of 
doubt the tube should be returned to the incubator. 
The colonies of the typhoid bacillus and the bacillus colt 
are whitish and opalescent. They usually have an 
angular or polygonal appearance when small, and tend 
to run together when older if they are thickly set. 
Their discrimination must be left to an expert. 
The bacillus of plague forms white colonies which are 
circular or have a crenated outline; they tend to run 
together and form a uniform film over the surface of the 
medium. 
The gonococcus, if it develops, forms very minute 
transparent colonies which have been compared to 
droplets of dew. They do not become confluent. 
This organism will not grow if transplanted on to 
the surface of ordinary media unless a thick film of 
blood be previously spread over it. 
After cultures have been obtained they are to be 
examined microscopically by the method described on 
page 29, and the morphological appearances compared 
with those of the pathogenic organisms which we have 
enumerated. It is especially important to test whether 
the organism which has been isolated, stains by Gram’s 
method or not. 
SECTION CUTTING. 
The methods employed in section cutting are some- 
what outside the scope of this work, inasmuch as 
sections are rarely necessary for the purposes of bacterio- 
