ISOLATION OF SPECIFIC PATHOGENES 85 



was then centrifuged, and the precipitate suspended in a 

 small amount of water and plated on Drigalski-Conradi 

 medium. Nieter (Nieter, 1906) made 20 parallel experi- 

 ments, using very pure water infected with typhoid 

 bacilli in varying numbers. By precipitating with ferric 

 sulphate and sodium hydrate, centrifuging, and then 

 filtering through a sterile filter he obtained small 

 numbers of bacteria. Using iron oxychloride as the 

 precipitant, he confirmed the results of Miiller. By 

 plating on malachite green agar he was often able to 

 get positive results when the Drigalski-Conradi medium 

 failed. 



By use of a combination of enrichment and chemical 

 precipitation, Ditthorn and Gildemeister (Ditthorn 

 and Gildemeister, 1906) isolated the typhoid bacillus 

 from enormous artificial dilutions in water. In the 

 typhoid fever epidemic in Posen, in 1906, it was found 

 that the bile of those dying from the disease contained 

 nearly pure cultures of typhoid bacilli. This led the 

 authors mentioned to use bile and bile agar as enrich- 

 ment^media. After precipitating by Miiller's method, 

 the whole of the precipitate was added to 100 

 c.c. sterile ox bile and grown at 37 for 24 hours, 

 after which time i c.c. portions were plated. With 

 extreme dilutions it was found desirable to incubate 

 for 48 to 72 hours. The results were unsatisfactory 

 in the presence of large numbers of water bacteria. 

 It is also pointed out that the iron oxychloride is 

 bactericidal in 48 hours. 



Separation on the Basis of Motility. Drigalski (Dri- 

 galski, 1906) has suggested the separation of B. typhi 



