90 AIDS TO BACTERIOLOGY 



becomes, therefore, necessary to enunciate definitely 

 those attributes which, if possessed by an organism, will 

 entitle it to be regarded as a colon bacillus. Of course 

 when a pathogenic organism of this class is isolated from 

 a patient, the name it is called by in the present state of 

 knowledge matters little so long as it prove corpus delicti. 

 But when estimating the organism to ascertain existence 

 of fsecal contamination a reasonable degree of definition 

 is necessary. Different bacteriologists select different 

 characters to which they require an organism to conform 

 before identifying it as typical B. coli. Houston described 

 an organism as ' flaginac ' if it produced a fluorescent 

 greenish yellow in neutral red glucose peptone-water (fl), 

 acid and gas in lactose (ag), indole in peptone-water (in], 

 and acid and curd in milk (ac). MacConkey suggests the 

 omission of tests for the growth on gelatin, action on milk, 

 glucose, and neutral red, and the indole test. In the place 

 of them he recommends the action of the organism on (1) 

 dulcite, (2) adonite, (3) inulin, and (4) the Voges and 

 Proskauer reaction. 



A negative indole reaction becomes more significant 

 when the para-dimethyl-amido-benzaldehyde test has 

 been used instead of nitrite and acid. 



It is possible, but by no means certain, that certain 

 varieties of the colon bacillus are of greater significance 

 as indicators of excretal contamination than others. The 

 presence or absence of power to ferment saccharose is 

 particularly thought worthy of emphasis in this connection, 

 and Houston denominates those fermenting saccharose, 

 producing acid and gas in lactose peptone water, and 

 giving an indole reaction as ' sagin ' organisms. Those 

 having no action on saccharose, but giving the other two 

 tests, are similarly christened ' agin ' bacilli. The bacillus 

 producing acid and gas from cane-sugar (saccharose) has 

 also been called B. coli communior by Durham, and this 

 variety is supposed to be of more recent intestinal ancestry 

 than another not fermenting saccharose. 



The American Committee mention the following 

 attributes as defining the colon group : ' Fermentation 

 of dextrose and lactose with gas production, short bacillus 

 with rounded ends, non- spore-forming, facultative anae- 

 robe, gives positive test with esculin, grows at 20 on 

 gelatin and at 37 on agar, non-liquefying in fourteen days 



