TEXT-BOOK OF BACTERIOLOGY. 231 



rules: After drying the cover-glass and drawing it three times 

 through the flame, add a number of drops of carbol-fuchsin, and 

 heat the same a number of times over a Bunsen burner until evap- 

 oration. After a short washing in water decolor in nitric acid and 

 treat further with 70$ alcohol, water, methyl-blue and water. 



With this method we shall in most cases succeed, and it is un- 

 necessary to describe separately the numerous other methods which 

 differ in some one or other point from the above-described proced- 

 ure. Only one other for specially staining tubercle bacilli will be 

 mentioned. This was first described by B. Fraenkel and later by 

 Gabbett without essential changes. It involves a new basis of pro- 

 cedure, and for practical purposes, where a rapid and simple exam- 

 ination of the expectoration for bacilli is desired, it may perhaps be 

 recommended as the best procedure. 



The manner of decoloring and counter-staining heretofore men- 

 tioned is here combined. The second color is united with the diluted 

 acid, and in consequence does away with all the intermediate steps 

 of the former procedure. 



Stain with hot carbol-fuchsin in the usual way, then place the 

 cover-glass without further preparation in the second solution. 

 This is a mixture of dilute nitric acid and alcoholic methyl- blue, 

 formed of 50 parts water, 30 of aicohol, 20 of nitric acid and methyl- 

 blue to saturation. The acid removes the fuchsin and leaves it only 

 in the bacilli; the decolored parts, however, now at once take up the 

 new stain (the methyl-blue), and in a short time the preparation 

 appears to the naked eye uniformly blue; it is then washed in 

 water and examined, the rods appearing red upon a blue ground. 



The essential point in this, as in the previous procedure, is, of 

 course, decoloration by the acid, which is resisted only by the tuber- 

 cle bacilli; these are, therefore, distinguished from all other bac- 

 teria by a specific staining. 



We know but one regular exception accessible to this staining 

 process, viz., the lepra bacilli. They are nearly related to Koch's 

 bacilli, but, unlike the latter, they take the usual watery anilin 

 stains equally as well as other bacteria, and thus present a very 

 remarkable tinctorial difference. 



The tubercle bacilli, it is true, are hot quite as refractory to 

 simple color solutions as was formerly supposed. By spreading a 

 pure culture upon cover-glasses and treating them (for twenty-four 

 to forty-eight hours) with watery fuchsin or gentian-violet, we will 

 find that a large portion of the bacilli has been stained. Some, 

 it is true, are not stained at all, some but imperf ectty ; but this 

 fact proves that, as to staining, no very great contrast exists 



