178 CLINICAL BACTERIOLOGY AND 



needle over a grease-free slide. If the film is too thin, it 

 should be allowed to air-dry, and another layer spread on 

 the top of it, this process being repeated if necessary. 

 In the examination of urine or of the watery secretion of 

 a badly diseased udder, this is sometimes needful. 



When the film has become dry, it should be passed two or 

 three times through the flame to fix it. 



The slide is then placed upon a metal tray under- 

 neath which is a lighted spirit lamp, and carbol-fuchsin 

 filtered on to the specimen. 



As soon as steam begins to rise from the slide, it should 

 be removed and decolorized by dipping in a 25 per cent, 

 solution of sulphuric acid for three or four minutes. This 

 has the effect of removing the stain from everything except 

 the acid-fast bacilli. The whole film now shows a yellow 

 tinge. It is then washed in water, when a pale red colour 

 returns to it. 



Wash in alcohol until no more stain comes away. By 

 doing so the stain is removed sometimes from acid - fast 

 bacilli other than tubercle, if present, which is of course to 

 be desired. 



Wash in water, counter-stain in weak methylene blue 

 for one minute. Wash again in water, and then dry 

 and mount. 



By this method the acid-fast bacilli are stained red, 

 while the non-acid-fast bacteria, tissue cells, leucocytes, etc., 

 are stained blue after the contrast stain. 



Pappenheim's Method. — This method is credited with 

 the power of differentiating between the bacillus of tuber- 

 culosis and other acid-fast bacteria. 



The specimen is prepared in the usual way, and stained 

 with filtered carbol-fuchsin without heat for three minutes. 

 The stain is now poured off the specimen, and corallin 

 solution applied ; excess of the fluid is then poured off and 

 another application made. Three or four applications in 

 all should be used. It is then washed in water, dried, and 

 mounted. 



