76 Elements of Water Bacteriology. 



structive action. Willson (Willsoii, 1905) suggested the 

 use of alum as a precipitant. He added 0.5 gr. alum per 

 liter of water examined. The mixture was then cen- 

 trifugalized, and the precipitate suspended in a small 

 amount of water and plated on Drigalski-Conradi medium. 

 Nieter (Nieter, 1906) made 20 parallel experiments, using 

 very pure water infected with typhoid bacilli in varying 

 numbers. By precipitating with ferric sulphate and sodium 

 hydrate, centrifugalizing, and then filtering through a 

 sterile filter he obtained results with small numbers of 

 bacteria. Using iron oxychloride as the precipitant, he 

 confirmed the results of Miiller. By plating on mala- 

 chite-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, Ditthom and Gildemeister (Ditthom 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 enrichment media. After 

 precipitating by Miiller's method, the whole of the pre- 

 cipitate was added to 100 c.c. sterile ox bile and grown 

 at 37 degrees for 24 hours, after which time i c.c. portions 

 were plated. With extreme dilutions it was found desir- 

 able to incubate for 48 to 72 hours. The results were 

 unsatisfactory in the presence of large numbers of water 



