TUBERCLE 67 



6. A metal (iron or copper) plate. The exact dimensions 

 do not matter, but 8 by 4 by J inches is a convenient size. It 

 should be mounted upon a tripod. This slab is not absolutely 

 necessary, but it is a very great advantage. 



Method We will suppose that the film has been prepared 

 by one of the methods described subsequently, allowed to dry, 

 and fixed by heat. 



1. Place the slide upon the metal plate, and heat the latter 

 by the flame. Flood the slide with carbol fuchsin, and let 

 the heat continue until the stain steams, but do not allow it 

 to dry up; let this go on for from three to five minutes. If 

 the stain shows signs of drying up, add a little more; if it 

 begins to boil, slide it along the plate away from the flame, 

 or remove the latter for a short time. 



If you have "no metal plate, it is possible to hold the slide 

 with a pair of forceps, but in this case the film is most con- 

 veniently made on a cover-glass. 



Remember not to let the stain dry up. 



2. Remove the slide from the plate with the forceps, and 

 wash it under the tap or in a bowl of water. 



3. Put it into the bottle containing the dilute acid. After 

 three or four minutes withdraw it and again wash. If much 

 pink colour comes back, re-insert it in the acid for a short 

 time, and again wash. The process must be repeated until 

 the film only shows a slight pink tinge. 



4. Now apply the methylene blue for half a minute or so. 



5. Wash, dry with blotting-paper, and then by gentle heat. 

 Apply a drop of balsam, and cover. If you are going to use 

 an oil-immersion lens, put on a drop of oil, but no cover-glass. 



Another Method. Filter into a test-tube sufficient carbol 

 fuchsin to flood the film, boil it over the Bunsen or spirit- 

 lamp, and pour it on to the film whilst still boiling. Let it 

 act until it is cool, when the bacilli will be found to be stained, 

 and the process of decolorization may be proceeded with. 



The times which are given above may be considerably 

 shortened in practice, but I do not advise this until consider- 

 able skill is acquired. Bacilli are much more easy to recog- 

 nize if they are deeply stained ; this is the reason for the pro- 

 longed staining, which may appear unnecessary to some. The 

 prolonged decolorization is an advantage, since it insures 

 that the tubercle bacilli shall be the only things left stained 



