NON-SPORING BACILLI 239 



1. Drigalski and Conradi's Medium. This is a meat 

 broth (1-5 Ib. per litre) to which, besides the peptone and 

 salt, i per cent of nutrose and 3 per cent of agar are added 

 and dissolved. Thereafter litmus solution is used to 

 dissolve pure lactose (quantity used = half quantity of 

 agar), and the whole is added to the hot agar fluid. Render 

 alkaline with sodium carbonate solution, and add a solution 

 of crystal- violet. The medium must not be overheated or 

 the lactose may be changed. It is a solid medium and is, 

 shortly, a lactose-nutrose-agar. 



The crystal-violet restrains the saprophytes. In 

 twenty-four hours B. coli colonies are red ; 2 to 6 mm. in 

 diameter, and non-transparent. B. typhosus colonies are 

 blue ; 2 mm. in diameter, and glassy and dew-like. 



The plates are inoculated by smearing the surface with 

 a glass rod, dipped in, say, diluted faeces. 



2. Endo's Medium. This is a 3 per cent agar neutralized 

 and then alkalinized with NaOH, and lactose and fuchsin 

 (basic) solution added, and then Na 2 SO 3 solution until 

 decolorized. Put into test tubes (15 c.c.), sterilize, and 

 keep in dark. When using, pour plates, and inoculate by 

 surface smears, when in twenty-four hours B. coli colonies 

 are red, and B. typhosus colonies are colourless. 



3. Loeffler's Medium. This is a 3 per cent agar to which 

 malachite-green is added, and this retards growth of B. 

 coli. B. typhosus colonies are minute glistening points ; 

 later, they colour agar yellow. 



4- Hoffman and Picker's Medium. Convert water sample 

 into medium by adding : caffein 2-5 per cent (restrains 

 B. coli) ; nutrose i per cent ; and crystal-violet o-ooi per 

 cent (restrains saprophytes). Incubate at 37 C. for not 

 more than 12 hours. The B. typhosus can then be isolated 

 on plate media. 



5. MacConkey's Media Have been already described on 

 page 153. The bile-salt assists growth of B. coli and 

 B. typhosus, and hinders others. Where neutral-red is 

 used, acid formation changes it to a rose-red. 



6. Bile Medium (for blood). 



7. Hiss's Agar-Gelatin Media, see p. 232. 



