230 Manual of Veterinary Microbiology. 



The preparations, cover glasses or sections, are left 

 for from two to five minutes in the fuchsin solution 

 heated as in the preceding methods, and then trans- 

 ferred to the second solution, in which they remain 

 one to two minutes. During this last period all the 

 elements other than the Koch bacilli are decolorized 

 under the influence of the nitric acid, but, at the same 

 time, fix the blue so that double staining is combined 

 with decoloration. 



The preparations are washed, dehydrated, and 

 mounted. 



All these methods have the same value in so far as 

 the coloration which they give is concerned. In prac- 

 tice, however, those solutions may be recommended 

 which are of longest preservation, and which require 

 the fewest manipulations. The method of Kitt es- 

 pecially fulfills these two conditions.* 



In the living subject about the only materials available 

 for examination are fluid products, such as nasal dis- 

 charge, milk or pus. In examining milk for tubercle 

 bacilli the cover glass, after drying and before staining, 

 should be freed from fatty matters by immersion in a 

 mixture of absolute alcohol and ether, or in chloro- 

 form. If a deposit is formed at the bottom of the 

 liquid this will furnish the best material for examina- 

 tion. 



Very often the Koch bacillus has to be sought for 

 in cadaveric products. In this case the investigations 

 will be directed to the tubercular lesions or those sus- 



* [Of the two methods most frequently employed — Ehrlich's 

 and Ziehl's— the latter, on account of the greater preservation 

 of the staining fluid, is often the most convenient, whilst the 

 former gives a more brilliant color to the bacilli. — B.] 



