THE RECOGNITION OF TYPICAL B. COLI 355 



The Recognition of typical B. coli. The work on b. coli, 

 especially in relation to its occurrence in water, has revealed 

 the existence of a very large number of varieties of the organism. 

 These differ from one another in the absence of one or more 

 of the characters which may be elucidated by the application 

 of the biological methods given. Considerable difference of 

 opinion exists as to what characters are to be looked upon as 

 type characters, i.e. characters shared by the greatest number of 

 varieties isolated. In this connection it is to be noted that as 

 the b. coli was originally isolated from the human intestine, and 

 as the detection of such intestinal bacteria outside the body 

 constitutes a most important practical question, the inquiry for 

 type characters is to a certain extent limited to an attempt to 

 arrive at the type most frequently present in the human intestine. 



Two standards may be alluded to. First, that of an English 

 Committee which reported in 1904 on the standardisation of 

 methods for the bacterioscopic examination of water. According 

 to this, the b. coli is a small, motile, non-sporing bacillus, capable 

 of growing at 37 C., decolorised by Gram, never liquefying 

 gelatin, producing clot and permanent acidity of milk within 

 seven days at 37, fermenting glucose and lactose, with, in both, 

 acid and gas formation, subsidiary points being the forma- 

 tion of indol, the formation of a thick yellowish-brown growth 

 on potato, production of fluorescence in neutral-red, reduction of 

 nitrates, and fermentation of saccharose. A similar American 

 Committee looked upon the typical organism as a non-sporing 

 bacillus, motile, fermenting dextrose-broth, with the formation 

 of about 50 per cent, of gas, of which about one-third is carbon 

 dioxide, causing acid and clot in milk in forty-eight hours, not 

 liquefying gelatin, producing indol and reducing nitrates. 

 These two standards differ in the fact that the English Committee 

 lay less weight on indol formation and the reduction of nitrates. 



Generally speaking, the application in any case of the scheme 

 of the English Committee is to be recommended, and organisms 

 conforming to the tests laid down may be accepted in the 

 majority of cases as probably having come from an intestinal 

 source. The further differentiation of organisms conforming to 

 this type will be dealt with later (p. 391). Meantime it may be 

 said that, in addition to the type characters, lactose-fermenters 

 from the human intestine usually ferment saccharose and dulcite 

 and have no effect on adonite, inulin and inosite, and it may be, 

 no influence on mannite. 



Pathogenic Properties of the B. coli. In man, the b. 

 coli has been found as the only organism present in various 



