ISOLATING THE TYPHOID BACILLUS. 451 



PRECIPITATION METHOD OF FiCKER. 1 The method 

 first proposed by Vallet, 2 and modified by Schuder, 3 for 

 the demonstration of bacillus typhosus in water consists 

 in the precipitation with sodium hyposulphite and nitrate 

 of lead, when the precipitate is dissolved with sodium 

 hyposulphite. This method was studied by Ficker, in 

 the laboratory, by adding to sterile river water definite 

 quantities of bacillus typhosus, but the results were not 

 satisfactory. The experiment showed that a portion of 

 the bacilli were not carried down with the precipitate, 

 while another portion were killed. These negative re- 

 sults led him to employ, at the suggestion of Hoffmann, 

 sulphate of iron as a precipitating substance, and the 

 sediment was dissolved with neutral potassium tartrate. 



The method employed is as follows : Two litres of 

 the water to be examined are placed into a narrow 

 sterile glass cylinder and rendered alkaline with 8 c.c. 

 of 10 per cent, soda solution, and afterward 7 c.c. of a 

 10 per cent, sulphate of iron solution are added and 

 mixed with the water by means of a sterile glass rod. 

 The cylinder is then placed in the ice chest. Precipi- 

 tation is complete in two to three hours. The over- 

 standing water is syphoned off, and the precipitate or 

 portions thereof are poured into sterile test-tubes. To 

 this precipitate is now added about a half volume of a 

 25 per cent, solution of neutral potassium tartrate. The 

 test-tube is closed with a sterile rubber cork and the 

 mixture thoroughly agitated, whereby the precipitate is 

 completely dissolved. With a sterile pipette one part 

 of the mixture is mixed in a test-tube with two parts 



1 Ficker: Hygienische Rundschau, 1904, Bd. xiv., S. 7. 



2 Vallet: Arch, de med. exp. et d'anat. path., 1901. 



3 Schiider : Zeitschr. fur Hygiene, Bd. xlii., S. 317. 



