122 A MANUAL OF BACTERIOLOGY 



paper, or the film may be allowed to dry spontaneously 

 in the air, in which case it should always be set up on 

 edge to drain. The preparations must be completely dried 

 before being mounted in balsam. 



Stained films tend to fade when mounted in Canada 

 balsam unless this be neutral in reaction. It may often be 

 better, therefore, to preserve unmounted. 



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

 lines may be made across the slide with a grease pencil 

 or with a stiff grease made by melting together vaseline 

 and paraffin wax, 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 organ- 

 isms, various expedients may be adopted. One is to 

 stain for a short time with a solution which does not give 

 a very dense colour, such as Loffler's methylene blue, or 

 by Gram's method if the organism stains by it ; this 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 

 sarcinse, but the staining agent should be anilin gentian 

 violet or dilute carbol-fuchsin and not Loffler'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 may be examined in water with the 



