MORPHOLOGY 395 



the result of an anterior poliomyelitis (Gilbert and Lion) ; this affection of the cord 

 is not necessarily fatal, and the rabbits sometimes recover even though the symptoms 

 may have been very marked. 



SECTION II. MORPHOLOGY. 

 1. Microscopical appearance. 



The colon bacillus, like the typhoid bacillus, is a small rod-shaped organism 

 with rounded ends. Morphologically, the two organisms are identical and 

 subject to the same variations ; spindle-shaped forms and pseudo-sporing 

 forms are met with equally in the two cases. 



Staining methods. Like the typhoid bacillus, the colon bacillus is gram- 

 negative and stains with the ordinary dyes. 



Mofility. As a rule, the colon bacillus is less motile than the typhoid 

 bacillus. 



The motility varies greatly in strains from different sources ; in some cases indeed 

 the bacilli are non-motile, in others the movements are slow and limited, while 

 in others again the organisms are almost as motile as the typhoid bacillus. 



Flagella. The flagella of the colon bacillus offer many points of contrast 

 with those of the typhoid bacillus. They can be stained by the same methods 

 as the latter but successful preparations are more difficult to obtain. 



The number of flagella is always smaller than in the case of the typhoid 

 bacillus : the colon bacillus has usually about four to six flagella and it is 

 quite the exception to find as many as twelve. 



The flagella may be arranged all round the surface [peritrichous ] : but 

 more commonly they are seen arranged in one or two bunches attached to 

 points on the surface, generally towards one end [lophotrichous]. The 

 flagella rarely exceed 3~5ft in length being only an half to a third as long as 

 those of the typhoid bacillus : they are not so wavy and undulating and are 

 never seen in the tangled bunches so characteristic of the typhoid bacillus. 



2. Cultural characteristics. 



A. Conditions of growth. The conditions under which growth takes place 

 are the same for the typhoid and colon bacilli : both are able to grow at 

 45 C., but given equal opportunities the colon bacillus grows rather more 

 quickly. Its growth is accompanied by an unpleasant faecal odour which is 

 characteristic of the organism. 



B. Characteristics of growth on various media. 1. Broth. In cultures 

 incubated at 37 C. growth is visible in 6-8 hours and has in general the same 

 characteristics as the growth of the typhoid bacillus ; a greyish pellicle 

 however often forms on the surface of the medium which is only exceptionally 

 seen in cultures of the typhoid bacillus. 



2. Gelatin. The colon bacillus does not liquefy gelatin. 



(a) Stab cultures. In cultures incubated at 20 C. growth is visible in 

 24 hours. The small colonies which form along the line of the stab become 

 opaque and soon unite to form a continuous line of growth. On the surface, 

 a thick whitish pellicle of creamy consistence forms and may extend to the 

 side of the tube. In short, the growth of the colon bacillus is, as a rule, both 

 more copious and more rapid than that of the typhoid bacillus but the dif- 

 ferences may not be very marked and cannot be relied upon for purposes of 

 differentiation. 



(/5) Stroke culture. After incubating for 30 hours a thin, bluish layer 

 with pinked edges appears which subsequently becomes whitish and opaque. 



