318 WATER HYGIENE 
material such as feces and urine. The reader is also referred to the 
methods developed for the isolation of B. typhi from feces. 
Drigalski and Conradi Method (1902). The preparation of the 
medium for this method has been described in the chapter on the 
media. The medium is solidified in Petri dishes which are allowed to 
become thoroughly dry before use. This may be accomplished by 
allowing the plates to stand at room temperature with the covers sus- 
pended above or in the 37° C. incubator. The surface is then streaked 
with the sample by means of a sterile bent glass rod. It is often a good 
plan to concentrate the water, either by reduced pressure of filtration. 
Bacillus colon forms red opaque colonies on this medium while Bacillus 
typhosus forms a blue and often transparent colony. Suspicious col- 
onies must be subcultured into other media and a complete cultural 
and morphological study made. Identification must be confirmed by 
agglutination reactions. 
Endo’s Medium. The preparation of this medium has been described 
in another chapter. The sample of water is streaked over the surface 
and the plates incubated at 37° C. for about fifteen hours. At the end 
of this time the Bacillus colon colonies will be red with possibly a metallic 
appearance, while the Bacillus typhosus colonies will be colorless. The 
same will be true with regard to the paratyphoid colonies. These sus- 
picious colonies should be subcultured into other media and a con- 
firmatory test made by means of the agglutination reactions. 
Kligler (1917) has shown that a differentiation in the typhoid- 
paratyphoid group may be made by means of hydrogen sulphid forma- 
tion and gas formation in the following medium which is semi-solid. 
1. Meat infusion agar containing ¢ or 1 per cent of agar (depending 
on the moisture content of the agar shreds). 
2. 0.1 per cent of glucose. 
3. 0.05 per cent lead acetate. 
The agar is prepared in the usual way except that the amount of agar 
is reduced. The sugar and lead acetate are dissolved in water sepa- 
rately and added to the sterile agar. The agar should be cooled to 60° C. 
in order not to precipitate the peptones. Stab inoculations are made. 
Strains of B. typhi brown the medium along the line of inoculation. 
B. paratyphi B. causes browning and gas formation; B. paratyphi A. 
causes gas but no browning. This has been confirmed by Jordan and 
Victorson (1917) who used a medium containing 1.5 per cent of agar. 
Morishima (1918) also described a similar method. The differentiation 
is secured in about the same way as with Kligler’s method. 
Russell’s medium may be used to good advantage with any of the 
