6o BACTERIOLOGY 



and to dehydrate. It absorbs the water rapidly and efficiently. 

 However, on account of its decolorizing tendency, it must be re- 

 moved before the specimens can be mounted permanently.) 



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

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



{h) Mount in Canada balsam. 



This method is riiore 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 and hyaline 

 material are stained blue, bacteria violet. It is often impossible 

 to decolorize the nuclei, completely 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 recognized. 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 carmine; the nuclei will then be colored red, bacteria violet. 



Tubercle bacilli may be stained in sections as follows : 



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

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

 without warming. 



(&) Wash in water. 



(c) Decolorize with some one of the decolorizing agents men- 

 tioned 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 color has dis- 

 appeared, which requires one-half to several minutes. 



{d) Wash in alcohol. 



(e) Wash in water. 



(0 Use hematoxylin as a contrast-strain for fuchsin prepara- 

 tions, and carmine for gentian violet preparations. (It is bet- 

 ter to stain with carmine first of all and before staining the bacilli. 

 The carmine is not affected by the subsequent treatment.) 



