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 7, 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 isnot 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.—1. 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, 5). 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 havea 
hanging-dyop specimen. The bacilli will be contained in 
the droplet of water (fig. 16, @) which hangs from the 
