CONTRAST STAINS: TUBERCLE STAINS. 101 



Iodine ...... 2 parts 



Potassium iodide .... 4 parts 



Distilled water . . . .100 parts 



P'or use, dilute with water to make a sherry-coloured solution. 



4. Wash in water. 



5. Decolorise in a saturated alcoholic solution of fluorescein (a 

 saturated solution in methylated spirit does equally well). 



6. Dehydrate, clear and mount. 



Contrast Stains. With all these methods it is often 

 advantageous, after decolorisation, to counterstain the tissues 

 with a dye different in colour from that retained by the 

 bacteria. 



Lithia carmine or alum carmine may be used for contrast-staining 

 in Gram's method. The sections here are stained first with the 

 contrast, and then treated by Gram's method. 



In the case of the following stains the contrast-staining is not carried 

 out till the tissues have been subjected to the bacterial stain and de- 

 colorised as far as possible. 



Safranin. Stock solution is a I per cent solution of safranin 

 dissolved in equal parts of methylated spirit and water. For use, dilute 

 one part with five of water, and stain for thirty seconds. 



Bismarck-broion. Stock solution saturated solution in equal parts 

 of alcohol and water. Stain for from two to three minutes. 



Both safranin and Bismarck-brown are excellent nuclear stains, and 

 in cases where Gram's method has been used, colour most of the 

 organisms which are left unstained by the violet. 



Eosin may be used as a i-iooo watery solution, and applied for 

 about a minute. It is a good ground stain, but does not bring out the 

 nuclei. 



After using a contrast stain, wash in water, dehydrate 

 rapidly, clear and mount. 



Stain for Tubercle and Leprosy Bacilli. These bacilli 

 cannot be well stained with a simple watery solution of a 

 basic aniline dye. This fact can easily be tested by attempting 

 to stain a film of a tubercle culture with such a solution. 

 They require a powerful stain containing a mordant, and 

 must be exposed to the stain for a long time, or the action 

 of the latter may be aided by a short application of heat. 

 When once stained, however, they resist decolorising with 

 very powerful reagents. Any combination of gentian-violet 



