jMirrotoiiir k'jih'es 



4.^) 



Figure 4. Microtome knije bevel as controlled by knife back. 



fit tight enough so that it does not move about on the knife. When it 

 shows considerable wear, buy a new one, because as the back wears the 

 cutting facets are widening. Do not ram the knife into the back; hold 

 the knife in one hand and the back in the other and work it on gradually 

 with a rocking motion. 



The importance of taking good care of a knife cannot be overem- 

 phasized. Clean it after use; some materials like blood and water, when 

 left on the knife edge, corrode it. Clean with xylene on soft cleansing 

 tissue and finally wipe it dry. Do not strike the edge with hard objects 

 (section lifter, dissecting needle); the edge can be damaged or dented. 



Sharpening Knives 



The glass plate has had the longest and most successful use as a sharpen- 

 ing instrument. In 1857 von Mohl used a thick glass plate; a rotating 

 one was developed by von Apathy in 1913, and a vertical one by Long 

 in 1927. Leather strops were advocated in 1922, and a couple of years 

 later carborundum hones, followed by finer grained hones or stropping 

 on canvas or leather. Many argue against a strop, saying that a knife 

 can be honed sharp enough for good sectioning. If, however, there are 

 fine serrations, gentle stropping frequently can remove them and im- 

 prove the cutting ability of the knife. 



If a glass plate is used, it should be at least fV oi an inch thick, 

 approximately 14 inches long, and an inch or two wider than a micro- 

 tome knife. Levigated alumina (approximately 1%) added to a neutral 

 soap solution is excellent for sharpening; the polishing should be done 



