.- EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 43 



(h) Add xylol; remove it with blotting-paper; and add fresh 

 xylol several times, in order to extract the last trace of aniline 

 oil. 



(i) Mount in Canada balsam. 



This method is more convenient for the staining of sections 

 than the Gram method. The results, however, are essentially 

 the same as far as the bacteria are concerned; fibrin is usually 

 stained blue, hyaline material is also stained blue, and bacteria 

 violet. It is often impossible to decolorize the nuclei com- 

 pletely without decolorizing the bacteria also. The parts of 

 the nuclei which remain stained often present pictures that 

 resemble bacteria, and which may lead to error if not recog- 

 nized. Basophilic granules also retain the stain, as do the 

 horny cells of the epidermis. These remarks apply also to 

 Gram's method, except as regards fibrin. Very beautiful 

 preparations can be obtained according to this or the Gram 

 method when the sections have previously been stained in car- 

 mine; the nuclei will then be colored red, bacteria violet. 



Where sections are stained with carmine they should be 

 thoroughly washed before applying the Gram stain, since the 

 presence of acid interferes with this stain,* and any of the acid 

 alcohol which is used after the carmine must be carefully re- 

 moved. 



Tubercle bacilli may be stained in sections as follows: 



(a) Use carbol-fuchsin, or aniline-water gentian-violet for 

 one-half to two hours with very gentle warming, or over night 

 without warming. See page 41 for the manner of handling 

 sections. 



(b) Wash in water. 



(c) Decolorize with some one of the decolorizing agents 

 mentioned in connection with the staining of tubercle bacilli in 

 cover-glass preparations, preferably 3 per cent, hydrochloric 

 acid alcohol. Decolorization must be continued until the red 



*Kolle and Wassermann. Vol. I., p. 70. 



