86 MICROSCOPIC EXAMINATION OF BACTERIA. 



Wash in water, dry, and mount. The tubercle bacilli are 

 stained a very brilliant red. 



Some experience is necessary before the tubercle bacillus 

 can be stained satisfactorily. Care must be taken that the 

 stain has acted sufficiently, and that the decolorizing agent is 

 not such in fact. It is impossible to overstain. Decoloriza- 

 tion with the dilute mineral acids is achieved in thirty seconds. 

 The film should always contain a sufficiency of stain. The 

 stain must be replaced if evaporation occurs. A 3 per cent, 

 alcoholic solution of hydrochloric acid is also a good decolor- 

 izer. Spirit of nitrous ether may be used. It is of agree- 

 able odor, and does not stain the hands, nor is it irritating to 

 the mucous membranes. When staining for tubercle bacilli 

 in sputum or other tubercular material, it should be borne 

 in mind that it is not always possible to find the bacillus in 

 the first specimen. Oftentimes as many as a dozen must be 

 made before it can be found. A negative result should never 

 be accepted as such until a large number of slides have been 

 examined. Neither should the bacillus be confused with other 

 organisms which have a strong resemblance to it. 



Gram's method is used for the differentiation of various 

 bacteria, especially the GONOCOCCUS. It is, therefore, very 

 frequently referred to as the gonococcus stain. A thin film 

 is prepared, dried in the air, and fixed in the flame. It is 

 stained for a few minutes with anilin-water gentian-violet. 

 The result will be better if the stain is warmed slightly. 

 Pour off the stain and immerse the specimen in Gram's solu- 

 tion. It has the following formula : 



Iodine crystals, 1 gram ; 



Potassium iodide, 2 grams ; 



Distilled water, 300 " 



Stain until the specimen turns a dark brown. Wash in 

 95 per cent, alcohol until color ceases to be given off and the 

 section is of a grayish color. Vesuvin or eosin may be used 

 as a counter-stain. Wash in water, dry, and mount iu Canada 

 balsam. By the action of Gram's solution on the bacteria 

 a compound is formed by the bacterial mycoprotein and the 



