710 A MANUAL OF BACTERIOLOGY 



inverted at 37 C. Colonies develop within twenty-four hours. 

 On the litmus media, B. coli colonies are large and pink ; strepto- 

 coccal colonies, small, delicate and pink ; typhoid and dysentery 

 colonies are small and blue. On neutral-red agar, B. coli and 

 streptococcal colonies are pink, the others are colourless. 



IDENTIFICATION OF, AND TESTS FOR, THE BACILLUS 

 COLI. Having obtained coli-like colonies on the plates 

 made from the preliminary cultivations of the water, 

 various tests must be used for identification. The organ- 

 ism should conform in morphology, motility and staining 

 reactions with the characters of the typical B. coli as given 

 at pp. 457-461, and must be subjected to various cultural 

 tests, e.g. the " flaginac " reactions of Houston (p. 460), 

 which the author generally employs. The majority of 

 human faecal B. coli give the flaginac reaction. If 

 atypical B. coli (see pp. 457 and 465) are met with, the 

 fact should be noted, but their significance is not yet 

 fully determined. Experience shows that if a water 

 yields glucose-fermenters, sooner or later it will contain 

 lactose-fermenters. 



STREPTOCOCCI. It is a distinct advantage to search 

 for streptococci. They may be looked for by making 

 hanging-drop preparations of the fluid media employed 

 for the preliminary cultivation of the B. coli (glucose or 

 lactose bile-salt peptone-water, etc. Glucose formate 

 broth or glucose neutral red broth incubated for forty to 

 forty-eight hours are the best). The presence or absence 

 of streptococci in these tubes gives also a quantitative 

 value to the examination, just as in the case of B. coli, 

 and the result obtained should be stated. The strepto- 

 cocci can be readily isolated on Conradi-agar plates. 



According to Houston (loo. cit.), faeces contain at least 100,000 

 streptococci per gramme. The type of streptococcus generally 

 present is one forming short chains, producing a uniform turbidity 

 in broth, acid and clot in litmus milk within five days at 37 0., 



