EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 41 



movement in stropping should be from toe to heel. Sections 

 should be cut to a thickness of not more than 25/4. Thinner 

 sections (5 to 10 1^) are to be desired. 



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

 basic aniline dyes is used — fuchsin, gentian-violet or methylene- 

 blue — made by adding one part of the alcoholic solution to 

 ten parts of distilled water. Loffer'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 or longer. 



(&) Wash in water. 



(c) Place in a watery solution of acetic acid, ^a P^^ cent., for 

 from a few seconds to 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 othe,: clearing 

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

 colors. It has the disadvantage of not clearing when the 

 slightest 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 of 

 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. 



The above statements apply to frozen sections or to sections 

 imbedded in celloidin. Paraffin sections are preferably at- 



