58 BACTERIOLOGY 



should be from heel to toe, always placing the back of the knife 

 next the hone when turning. The knife should be stropped fre- 

 quently. The leather of the strop should be glued to a strip of 

 wood to make a flat surface. The movement in stropping should 

 be from toe to heel. Sections should be cut to a thickness of not 

 more than 25 /*. Thinner sections (5 to 10 //) are to be desired. 



Staining of Sections. A watery solution of one of the aniline 

 dyes is used fuchsin, gentian violet or methylene blue made 

 by adding a few drops of the alcoholic solution to a dish filled 

 with water. Loffler's solution of methylene blue serves very 

 well. 



By this process most bacteria are stained; also the nuclei of 

 cells; frequently, also, certain granules contained within some 

 cells (German, Mastzellen), which may easily be mistaken for 

 bacteria by the inexperienced (basophilic granules). 



(a) Place the section in the staining solution from two to five 

 minutes. 



(b) Wash in water. 



(c) Place in a watery solution of acetic acid, i per cent for 

 one minute. 



(d) Alcohol, one to two minutes; change to absolute alcohol. 

 Touch the sections to blotting-paper to remove the superfluous 

 alcohol. 



(e) Xylol until clear; xylol is to be preferred to other clearing 

 agents, like oil of cloves, most of which slowly remove aniline 

 colors. It has the disadvantage of not clearing when more than a 

 trace of water is present; dehydration in alcohol must, therefore, 

 be complete. The section should be removed from the xylol as 

 soon as it is cleared; otherwise wrinkling occurs. 



(/) The section is placed upon a glass slide; a drop Canada 

 balsam is placed upon it and then a cover-glass. The Canada 

 balsam should be dissolved in xylol. 



The section is to be manipulated with straight or bent needles. 

 The removal from xylol to the glass slide is managed best with a 

 spatula or section-lifter. 



