STAINING OF BACTERIA IN TISSUES. 155 



avoided. This method, while it stains certain bac- 

 teria in tissues very satisfactorily, is nevertheless 

 designed especially for the staining of fibrin. Fibrin 

 and hyaline material will be stained deep blue, bacteria 

 a dark violet. 



Staining of Tubercle Bacilli in Tissues. — As 

 for tiie staining of cover-slips, only those methods most 

 commonly employed will be given. 



The method of Ehrlich. Stain the sections in aniline- 

 water fuchsin or gentian-violet for twenty-four hours ; 

 decolorize in 20 per cent, nitric acid for a few seconds 

 only, the color need not be entirely extracted ; then into 

 70 per cent, alcohol until no more color can be ex- 

 tracted by the alcohol ; stain as contrast color in dilute 

 watery methylene-blue, malachite-green, or Bismarck- 

 brown solution ; wash out in 90 per cent, alcohol, then 

 in absolute alcohol for a few seconds ; clear up in xylol 

 and mount in xylol-balsam. 



Method of Ziehl-Neelsen. Stain the sections in 

 warmed carbol-fuchsin solution for one hour ; tempera- 

 ture to be about 45° to 50° C. Decolorize for a few 

 seconds in 5 per cent, sulphuric acid, then in 70 per 

 cent, alcohol, and from this on as by the Ehrlich 

 method. 



Dry method. For the tubercle bacilli, as for many 

 other organisms in tissues, the following method may 

 be emjjloyed if only the presence of organisms is to be 

 detected and the histological condition of the tissues is 

 a matter of no consequence : Bring the sections from 

 water upon a slide or cover-slip, dry, fix, and stain by 

 the methods for cover-slip preparations. 



Gray's m^hod. The method employed by Gray at 

 the Army Medical Museum, Washington, D. C, a 



