532 APPLICATION OF METHODS OF BACTERIOLOGY 



While not generally considered a pathogenic organism, 

 there is, nevertheless, sufficient evidence to warrant the 

 statement that under favorable conditions of reduced vitality 

 on the part of the animal tissues, this organism may assume 

 pathogenic properties, so that its presence in diseased con- 

 ditions is not always to be considered as accidental, though 

 this is frequently the case. 



The morphological and cultural peculiarities of bacillus 

 coli are as follows : 



Morphology. In shape it is a rod with rounded ends, 

 sometimes so short as to appear almost spherical, while 

 again it is seen as very much longer threads. Often both 

 forms are associated in the same culture. It may occur as 

 single cells, or as pairs joined end to end. 



It has no peculiar morphological features that can aid 

 in its identification. It is usually said to be motile, and 

 undoubtedly is motile in the majority of cases; but its 

 movements are at times so sluggish that a positive opinion 

 is often difficult. 



By Loffler's method of staining, flagella can be demon- 

 strated, though usually not in such numbers as are seen to 

 occur on the typhoid fever bacillus. 



Cultural Characteristics. It grows both with and without 

 free oxygen. 



On the surface of gelatin its colonies appear as small, dry, 

 irregular, flat, blue-white points that are commonly some- 

 what dentated or notched at the margin. They are a trifle 

 denser at the center than at the periphery, and are often 

 marked at or near the middle by an oval or round nucleus- 

 like mass the original colony from which the layer on the 

 surface developed. When located in the depths of the 

 gelatin, and examined with a low-power lens, they are at 



