QUALITATIVE BACTERIOLOGICAL ANALYSIS. 163 



examined with the naked eye, the growth on agar at 37 C. is 

 almost as rapid as that of B. coli, and it is often impossible 

 to distinguish between colonies of B. coli and B. typhosus on 

 agar plates. Still, as a rule, the colonies of the latter organism 

 are much smaller and more transparent than those of the former. 



Gelatine-stab. On the surface there is a thin circumscribed 

 growth like a surface colony, and along the line of inoculation 

 a thin greyish growth appears, ending below in discrete white 

 masses. 



Gelatine-slope. A thin, narrow growth developes along the 

 line of inoculation ; the margin is slightly irregular, but not 

 so markedly crenate as the corresponding growth of B. coli. 



Agar-slope. A thin, greyish-white growth, usually more 

 transparent than that of B. coli. 



Potato. A smooth glistening film develops, which is often 

 difficult to recognise with the naked eye. If the potato has an 

 alkaline reaction, a faintly brownish coloured growth may 

 appear. 



Sugar Gelatine (Shake Culture). There is no formation of 

 gas in lactose media, but glucose-gelatine is said to be some- 

 times fermented. 



Witters Peptone and Salt Solution. After seven days in- 

 cubation at 37 C. there is, as a rule, no nitroso-indol reaction 

 when the medium is tested with 1 c.c. of potassium nitrite 

 (0*02^), and a few drops of pure sulphuric acid. Occasionally, 

 after standing some few hours, a faint rope tint is shown by 

 undoubtedly pure cultures of B. typhosus. 



Milk. After one month's incubation there is no change in 

 the appearance of this medium. 



Neutral-red Glucose-agar . In this medium, as a stab or 

 shake culture at 37 C., the B. typhosus produces no fluor- 

 escence or change in colour. One loop of a broth culture 

 of the suspected organism is added to the melted agar, cooled 

 to 40 C., when a shake is to be made. Scheffler recommended 

 0'3 gramme of glucose and 1 c.c. of a concentrated aqueous 

 solution of neutral-red, to be added to 100 c.c. of melted agar. 

 B. coli, when inoculated into this medium, produces a marked 

 greenish fluorescence after twenty-four, or at latest forty-eight. 

 hours incubation at 37 C. 



