40 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



taking care not to touch any part of the mouth, and replace it in 

 the tube. 



5. Withdraw the tongue depressor, and place it in the anti- 

 septic lotion or boiling water. 



6. Push the cork home into the tube. 



Method of examining the Swab. — This may be carried out by means 

 of stained films, prepared directly from the swabs, or by means 

 of cultures. The former method is less useful than the latter, 

 but we shall consider it first, as it can be performed by anyone 

 who possesses a microscope carrying a Jj^-inch oil-immersion 

 lens, and often gives valuable information. Moreover, it does 

 not take long, and but little delay is caused. 



Requisites. — i. Clean slides and cover-glasses. 



2. Stains. — Loffler's blue or carbol thionin, and aniline gentian 

 violet. 



3. Gram's iodine solution and alcohol — methylated spirit will do. 



4. Strips of white filter or blotting paper. 



5. Balsam. 



Method. — Prepare a film in the following way : Rub the swab 

 on the middle of a clean slide, so as to spread some of the secretion 

 into a thin layer on the surface. Allow it to dry, and fix it by 

 passing it slowly through the flame, until the upper surface is just 

 too hot to prevent your pressing your finger upon it in comfort. 

 Allow it to cool. 



Now filter a few drops of Loffler's blue or carbol thionin on 

 to the film, and allow it to act for two minutes. Wash under 

 the tap. 



Dry by pressing carefully with strips of blotting-paper, and 

 then in the flame. Place a drop of balsam upon the film, and 

 apply a cover-glass. 



Prepare a second film, and stain by Gram's method (p. 24), 

 counterstaining by dilute carbol fuchsin. 



The films are now examined microscopically (see p. 27). We 

 shall defer the description of the points upon which a diagnosis 

 is to be based until we deal with the examination of cultures. 



Cultural Methods. 



The diphtheria bacillus grows best at or near the body 

 temperature (about 37° C), and flourishes on almost all culture 

 media. But agar is scarcely ever used in growing it for diagnostic 



