METHOD OF EXAMINING CULTURES. 31 
the flame once or twice. This coagulates the albumen 
present and the bacteria are now fixed down so firmly 
that they will not be removed by subsequent washing. 
The exact amount of heat which should be used cannot 
be stated, as it varies according to the thickness of the 
slide, &c., and can only be determined by practice. It 
may be estimated roughly by pressing the finger upon 
the upper surface of the slide close to the film, but not 
touching it. The slide should be just uncomfortably 
warm to the finger, but not hot enough to burn it. 
11. Filter a few drops of the stain on to the surface 
of the film and allow it to act for the requisite time. 
Exact details will be given in each case. 
12. Next wash the slide under the tap, blot it with 
clean white filter paper, taking care to avoid rubbing, 
and heat it gently over the flame until absolutely dry. 
13. Place a drop of balsam on the film and apply a 
clean dry cover-glass. 
The preparation is now ready for examination. 
This also is a process which sounds more complicated 
than it really is. The steps are readily learnt, and the 
whole process (excluding the time spent in staining, 
which may be long or short), does not take more than 
two or three minutes. 
Most bacteriologists make their films on cover-glasses 
and not on slides. The steps are just the same, except 
that the cover-glasses, being much thinner, naturally 
require much less heating to fix the film; they are 
passed rapidly through the flame three times. It isa 
great advantage to use Cornet’s forceps in working with 
cover-glasses. These forceps are self-retaining, and 
hold the cover-glass in a horizontal position so that 
stains can be poured upon them whilst the forceps are 
resting on the table. But the staining can be carried 
