WATER 



solution large Petri dishes containing Drigalski-Conradi or other 

 suitable solid media are inoculated. 



Ficker claims that by this method there is very little loss of 

 typhoid bacilli ; 97 to 98 per cent, of those present being carried 

 down with the precipitate. 



(c) Concentration by sedimentation without chemical precipi- 

 tation. If a powerful centrifuge is available the water may 

 be directly centrifugalized and the deposit used for plating. 

 Houston 1 in some investigations upon typhoid bacilli in river 

 water used this method. In dealing with a raw water containing 

 72,000 bacteria per c.c. he was able to recover the typhoid 

 bacillus when 47 had been added to 100 c.c. of the water. 



(d) Concentration by evaporation wider reduced pressure. 

 Wilson 2 has described a method which enables water to be 



f r f~ r~T TTTt "f- H 



T rr 



Fig. 6, Wilson's apparatus for concentration under reduced pressure. 



1 Fifth Research Report, Metropolitan Water Board> 1910. 

 8 Brit. Mtd. fount. May 18, 1907. 



