388 A MANUAL OF BACTERIOLOGY 



(2) The organism may be isolated by plating on gelatin, agar, 

 litmus lactose agar, Conradi-Drigalski agar, or by the use of neutral 

 red or bile -salt media (see " Water "). The isolated organism must 

 be tested as to its morphology, motility, non-Gram staining, non- 

 liquefaction of gelatin, indole production, curdling of milk, and 

 fermentation of glucose, lactose, dulcitol, mannitol, etc. 



(3) An agglutination reaction may likewise be tried, but if nega- 

 tive is of little value, as there are so many varieties of the colon 

 bacillus, and one variety may not be agglutinated by the specific 

 serum obtained with another variety. A positive reaction must 

 also be carefully controlled, as the colon bacilus is much more 

 readily agglutinated by normal serum than is the typhoid bacillus. 



Varieties of Bacillus coli 



Organisms are frequently met with in faeces, manure, sewage and 

 polluted water which resemble the typical B. coli in many of their 

 characters, but which differ from it in certain particulars. Thus 

 the colonies on gelatin, instead of being smooth, may be wrinkled ; 

 milk may be but slowly curdled (three to eight days) ; acid or gas 

 production, or both, in sugars may be less marked than usual. 

 These organisms are generally regarded as varieties of the B. coli, 

 and are perhaps dervied from typical B. coli. There is, however, 

 little evidence that B. coli can be transformed into such varieties, 

 or that these varieties can be reconverted into typical B. coli ; 

 Revis (loc. cit.) has produced considerable alterations of fermentive 

 power, and in the characters of the colonies of certain coliform 

 organisms. 



Organisms that have been Regarded as 

 Variants of B. coli 



A number of organisms have been regarded as being varieties of 

 the B. coli (consult Table of fermentation reactions, p. 381). 



(1) Bacillus cavicida (Brieger). This resembles B. coli in most 

 of its characters, but was stated to be non-motile. MacConkey says 

 it is motile. 



(2) Bacillus neapolitanus (Emmerich). Isolated from the bowel 

 in cases of cholera. It differs from B. coli in not being motile, and 

 in fermenting cane sugar. 



(3) Gas-forming bacilli of Laser and Gartner. 1 



1 Oentr.f. BaJct (l te Abt.), xiii, 1893, p. 217 ; xv, 1894, pp. 1, 276. 



