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 is a 

 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 



