76 ELEMENTS OF WATER BACTERIOLOGY 



made in the development of new methods for isolating 

 the typhoid bacillus. These fall in three distinct 

 groups: first, the direct isolation by differential, fre- 

 quently colored, solid media; second, isolation as 

 above, preceded by enrichment methods; third, isola- 

 tion, with or without enrichment, preceded by concen- 

 tration of the organisms by agglutination with typhoid 

 serum or concentration by chemical precipitation. 



Isolation Methods, Using Solid Media. Drigalski 

 and Conradi (Drigalski and Conradi, 1902), prepared 

 a medium primarily for the isolation of typhoid bacilli 

 from excreta, which may also be applied in water 

 bacteriology. This consists of an agar medium 

 containing nutrose, sodium chloride, litmus, lactose, 

 and a dye, " crystal violet "; and it is used in the form 

 of plate cultures infected by smearing the surface with 

 a bent glass rod after thorough cooling. The culture 

 medium is a selective one, ordinary saprophytes fail- 

 ing to grow, while after 14 to 24 hours at 37, 

 colon and typhoid colonies can be readily distinguished 

 from one another. The colon bacillus produces red, 

 non-transparent colonies, of variable size and depth 

 of color, while the typhoid colonies are blue or violet, 

 transparent and of smaller size, seldom exceeding three 

 millimeters in diameter. 



Endo (Endo, 1904) has suggested the use of a fuchsin- 

 lactose-agar decolorized by sodium sulphite. Upon 

 this medium B. coli produces bright red, sharply defined 

 round colonies in 24 hours at 37, while B. typhi 

 gives round, colorless, transparent colonies with thin 

 margins. This medium has been somewhat modified 



