172 BACTERIOLOGY. 



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

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

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

 watched under the low power of the microscope. When 

 decolorization is sufficient (repeated applications of the 

 aniline oil and xylol mixture are generally necessary) 

 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 with 

 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 of Tubercle Bacilli in Tissues. — As 

 for the 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 extracted 

 by the alcohol; stain as contrast-color in dilute watery 

 raethylene-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-Neelsen. Stain the sections in warmed 

 carbol-fuchsin solution for one hour; temperature to be 

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



