FILM STAINING 107 



To prevent the stain flowing all over a slide, two lines 

 may be drawn across the slide with a grease pencil, one 

 on either side of the area to be stained. 



If there be much debris or other material which, when 

 stained, would interfere with a clear view of the organisms, 

 various expedients may be adopted. One is to stain for 

 a short time with a solution which does not give a very 

 dense colour, the best for this purpose being Loffler's 

 methylene blue, or Gram's method may be made use of 

 if the organism stains by it, and will give the best result 

 of any. Another plan is to treat the specimen with acetic 

 acid before staining ; it may be just dipped in glacial 

 acetic acid and immediately washed in distilled water, or 

 immersed in 20 per cent, acetic acid for five to ten minutes, 

 washed in distilled water, and then stained. A third is, 

 after staining and washing, to rinse the preparation in 

 dilute alcohol (alcohol 1 part, water 1 or 2 parts), and 

 immediately to wash again in water to stop the further 

 action of the alcohol. If the film be thick, two or three 

 rinses in the dilute alcohol may be necessary. This process 

 gives excellent results with the sarcinae, but the staining 

 agent should be anilin gentian violet or dilute carbol- 

 fuchsin and not LofHer's blue, unless it is allowed to act 

 for fifteen to twenty minutes. The treatment with acetic 

 acid before staining may be combined with decolorisation 

 with alcohol after. 



Preparations can always be examined in water with the 

 J-in. objective, after washing and before permanently 

 mounting, in order to see whether they are satisfactory. 

 If the film is on a slide, a drop of water is put on and 

 covered with a cover-glass, if on a cover-glass, this is 

 mounted in a drop of water on a slide. If satisfactory, 

 the preparation can be dried, and mounted in balsam ; or 

 if not stained sufficiently, or if stained too deeply, it can be 

 stained again, or further decolorised, as the case may be. 



