QUALITATIVE BACTERIOLOGICAL ANALYSIS. 



if the failure to find the B. typhosus in the Pregel water was 

 due to the presence of the B. coli. With this end in view he 

 mixed equal quantities of B. coli and B. typhosus in " pipe- 

 water," and also added typhoid stools, which were known to 

 contain B. typhosus, to the " pipe-water. 11 The waters thus 

 polluted were investigated by Mankinds method, with the results 

 shown in the following table : 



It is evident from these experiments that Hankin''s method 

 will fail to detect the B. typhosus in water supplies polluted 

 with typhoid excreta. If, however, a water supply were 

 polluted only with urine, in which case the B. coli is usually 

 absent, the method would probably succeed in demonstrating 

 the B. typhosus, but under these conditions most of the other 

 methods would also be successful, and the case of a water-supply 

 being only polluted with urine so seldom occurs in actual 

 practice that Mankinds method must be considered of limited 

 value. 



Piorkowski has lately recommended a method for isolating 

 the B. typhosus, which has been successfully used to determine 

 the presence of this organism in typhoid stools. A special 

 medium is employed, which is made by allowing ordinary urine 

 (specific gravity 1020) to turn faintly alkaline; 3*3 per cent, 

 gelatine and 0'5 per cent, peptone are then added, and the 

 medium sterilised in the "steamer" on three successive days. 

 After fifteen hours at 22 C. in this medium B. typhosus grows 

 into characteristic flagellated or Ramosus-like colonies, while the 

 B. coli appears only as round colonies, from which at times 

 short, plump processes may run out into the gelatine. Working 



