EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 41 



to the slide, and is less likely to wrinkle. It must not be allowed 

 to dry. 



Gram's method may be applied to the staining of sections 

 of tissues as well as to smears upon cover-glasses. 



(a) Place the section in aniline-water gentian-violet, one to 

 five minutes. See the preceding paragraph for the manner of 

 handling sections. 



(b) Rinse briefly in water. 



(c) Iodine solution (see page 30), one and one-half minutes. 



(d) Alcohol, until decolorized to a faint blue-gray. 



(e) Xylol. 



(/) Mount on a slide in balsam. 



Weigert's Modification of Gram's Method, or Weigert's 

 Stain for Fibrin. — (a) Place the section in aniUne-water 

 gentian-violet solution, five minutes or more. See page 40 for 

 the manner of handhng sections. 



(6) Wash briefly in water. 



(c) After placing the section upon a slide, and having straight- 

 ened it carefully, absorb the water with blotting-paper. 



(d) Iodine solution (see page 30), one to two minutes. 



(e) Absorb the iodine solution with blotting-paper. 



(/) Add aniline oil, removing it from time to time with blot- 

 ting-paper, and adding fresh aniline oil until the color ceases to 

 come away. (Aniline oil serves in this connection both to 

 decolorize and to dehydrate. It absorbs the water rapidly and 

 efficiently. However, on account of its decolorizing tendency, 

 it must be removed 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 more convenient for the staining of sections 

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

 S 



