88 BACTERIOLOGICAL DIAGNOSIS. 



2. A small funnel provided with a double thickness of 

 white filter paper. This is unncessary if dead cultures 

 are to be used. 



3. Three clean watch-glasses. 



4. A platinum loop. This should be made of fine 

 wire and have a loop (which must be completely closed) 

 about ^y in. in diameter. 



5. A hollow-ground slide. This is an ordinary slide 

 having a well about half an inch in diameter sunk in its 

 centre. If it is not at hand a cell may be built up on 

 an ordinary slide. Take a piece of thin card one inch 

 square and cut out a square half an inch in diameter 

 from its centre. Fix this perforated square down on 

 to the slide with vaseline or immersion oil. 



6. Thin cover-glasses. 



7. The microscope. The test can be carried out 

 quite well with a ^ in. lens. 



Process. i. Making the emulsion. Pour a small quan- 

 tity of tap water into the culture tube, or better, 

 scrape off some of the growth and mix it with some 

 water in a watch-glass. In either case stir it round 

 with the platinum needle for a few minutes so that the 

 bacilli are evenly distributed throughout the water and 

 form an emulsion. 



Next take the hollow-ground slide and paint a ring of 

 immersion oil round the well (fig. 16, b). If you are 

 using a built-up cell paint the top of the card with the 

 oil. In either case vaseline may be used. 



Place a drop of the emulsion on a clean dry cover- 

 glass and invert the hollow ground slide over it ; press 

 it down so that the oil round the well adheres to the 

 cover-glass ; now invert the slide and you will have a 

 hanging-drop specimen. The bacilli will be contained in 

 the droplet of water (fig. 16, a) which hangs from the 



