METHODS OF EXAMINATION 127 



between apparatus, is bent to a U form in the flame, and both 

 ends are drawn out to points, after which it is sterilised and 

 sealed hermetically at both extremities while still hot. At 

 the place where water is to be collected both ends are broken 

 off, and one held in the water while suction is exerted at the 

 other until the tube is full, when both points are sealed on 

 the spot. The tubes are sent packed in ice. 



Other methods. — To gain some preliminary information 

 as to what micro-organisms are present, a few drops of the 

 water to be examined are evaporated on a cover-glass, which 

 is drawn several times through the gas flame to fix the dry 

 residue and covered with one or two drops of a staining 

 solution. In washing off the stain, the stream from the 

 wash-bottle should not be directed on the actual deposit 

 from the water. 



It is advisable that every examination by culture should 

 be preceded by sedimentation, for which purpose Finkelnburg 

 has contrived an apparatus consisting of a cylindrical vessel 

 with a bottom capable of being lifted out. Water being 

 allowed to drop in through an opening in the bottom which 

 can be closed by a glass tap, the floating particles gather 

 on the movable bottom of the glass, and in this way a de- 

 position of the organised impurities can rapidly be obtained. 

 Csokor's or Gartner's centrifugal machine serves this pur- 

 pose still better. In order to isolate the bacilli of cholera 

 and typhoid and other bacteria endowed with motility, Ali 

 Cohen has brought forward a peculiar method depending 

 on the chemotadlc action of certain stimulating substances, 

 especially of the juice of raw potatoes. A small glass 

 capillary tube is filled with the fluid found on the cut sur- 

 face of the raw potato, and is sealed at one end. A ridge 

 of paraffin is now made on a microscope slide, enclosing a 

 space into which the fluid to be examined is introduced, 

 and the sealed end of the capillary tube is fixed in the 



