EXAMINATION OF BACTERIA WITH THE MICROSCOPE. 5! 



vice for elevating the object which is to be cut any desired 

 distance after each excursion of the knife. The thickness 

 of the section will be the distance which the object is ele- 

 vated. The knife is kept wet with alcohol during the cut- 

 ting of collodion sections, otherwise it is left dry. The 

 microtome is usually provided with a special form of knife. 

 A razor will serve nearly as well, after having had the 

 lower side ground flat. If a razor is used, a special form 

 of razor-holder must be attached to the microtome to re- 

 ceive the razor. Above all, it is necessary that the knives 

 should be kept in good condition. Only occasionally will 

 they need honing, using a fine water-stone or Belgian 

 hone. The movement in honing should be from heel to 

 toe, always placing the back of the knife next the hone 

 when turning. The knife should be stropped frequently. 

 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 io/*) 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, Mastzcllcn}, 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. 

 5 



