DESCRIPTION OF SPECIES 



411 



poran-, and is succeeded by alkalin- 

 ity (Petruschky). 

 Aerobic or facultative anaerobic. 

 Vitality — Thermal death-point, 

 60° C. in 10 minutes, more hardy 

 than B. typhosus but not highly 

 resistant. 



Pathogenesis — B. coli may be 

 pathogenic in association with 

 other bacteria ; it has been held to 

 be the cause of epidemic diarrhoea, 

 and plays a part in pneumonia, 

 suppuration, etc. 

 Remarks — Whilst the above descrip- 

 tion applies to the normal type of B. 

 coli, it should be clearly understood 

 that a large number of bacilli have 

 been described which possess some, 

 but not all, of the above characters. 

 Refik has described {Ann. de VInst. 

 Pasteur, x., 1896, 242), 5 varying types 

 very similar to the normal B. coli, but 

 differing in one or more characters. 

 Almost all forms, however, have some 

 features in common, e.g. motility, few 

 flagella, and characteristic gro\vth on 

 potato. Moreover, there are a group 

 of organisms allied to B. coli, and often 

 associated with it. Like it also they 

 are related etiologically or otherwise to 

 similar pathological processes. Refik's 

 types are briefly as follows : — 



A. Ferments lactose, coagulatesmilk, 



but no indol reaction. 



B. Ferments lactose, does not coagu- 



late milk, gives indol reaction. 



C. Ferments lactose, does not coagu- 



late milk, does not give indol 

 reaction. 



D. Does not ferment lactose, coagu- 



lates milk, does not give indol 

 reaction. 



E. Does not ferment lactose, does 



not coagailate milk, does not 

 give indol reaction. 



Roux, Rodet, and others have stated 

 that B. coli, under certain circum- 

 stances, may assume a character not 

 distinguishable from B. typhosus, both 

 in its biological and culttrral character- 

 istics, and in its pathogenic properties. 

 Klein and other bacteriologists, as the 

 result of numerous experiments, have 

 been unable up to the present to effect 

 any transformation of one form into the 

 other. Each organism has retained 

 unimpaired its differential characters. 



The virulence of B. coli is affected 

 by:- 



1. The pathological condition of 



intestinal canal. 



2. Increased by passing through a 



guinea-pig. 



3. Attenuated by age. 



The chemical properties of its pro- 

 ducts are among its most striking 

 features. 



The following are the differences 

 between B. coli and B. typhosus 

 usually relied upon for diagnostic 

 purposes : — 



Comparative Features of B. coli and B. typhosus. 



B. typhosus. 

 Morphology — Bacillus of unequal lengths ; some 



filaments. 

 Flagella — Long, wavy, spiral, numerous (9 to 



18) ; movement very active. 



On gelatine and agar — Angular, irregular, 

 slightly raised colonies ; slow growth ; 

 medium remains clear. 



In gelatine — In ordinary gelatine and in lactose 

 gelatine no gas is produced (at 20° C). 



B. coli. 



Bacillus shorter and thicker ; filaments 

 rare. 



Shorter, stiffer, few (average 3) move- 

 ment less active, and sometimes almost 

 absent. 



Colonies with even margin, homogeneous, 

 much larger and quicker growth, 

 medium becomes turbid or coloured 



Under the same circumstances abundant 

 gas is produced. 



