STAINING TUBERCLE BACILLI IN TISSUES. 193 



ble with filter-paper, and then decolorized with a mixt- 

 ure of aniline oil (one part) and xylol (two parts). 

 This is the delicate part of the process, and can be 

 watched under a low power of the microscope. When 

 decolorization is sufficient (repeated applications of the 

 aniline oil and xylol mixture are 'generally necessarj^) 

 pure xylol replaces the mixture, and the specimen is 

 finally mounted in xylol-balsam. Unless all the ani- 

 line oil is replaced by the xylol the specimen will not 

 keep well. In this process the aniline oil is really the 

 decolorizer, and has the valuable property of absorbing 

 a certain amount of water, so that dehydration M'ith 

 alcohol is avoided. This method, while it stains certain 

 bacteria in tissues very satisfactorily, is nevertheless de- 

 signed especially for the staining of fibrin. Fibrin and 

 hyaline material will be stained deep blue ; bacteria a 

 dark violet. 



Staining Tubercle Bacilli in Tissues. — As in 

 the case of cover-slips, only those methods most com- 

 monly 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 in 

 70 per cent, alcohol until no more color can be extracted 

 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 abso- 

 lute alcohol for a few seconds ; clear up in xylol and 

 mount in xylol-balsam. 



Method of Ziehl-Neeken. Stain the sections in warmed 

 carbol-fuchsiri solution for one hour ; temperature to be 

 about 45° to 50° C. Decolorize for a few seconds in 5 



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