372 MICROTOMES AND SECTION KNIVES [Cn. XI 



is set obliquely and there results an oblique or drawing cut, as in 

 whittling. 



605. Section knives. A section knife should have the following 

 characters, (i) The steel should be good. (2) The blade should be 

 slightly hollow ground on both sides. Why some makers persist in 

 grinding one side flat is a mystery. (3) The edge of the knife should 

 be straight, not curved as in a shaving razor. (4) The back should 

 be parallel with the edge. (5) The blade should be long, 12 to 15 

 centimeters, as it takes no more time or skill to sharpen a large than 

 a small knife. (6) The blade should be heavy. There was formerly 

 a fashion of making very thin-bladed section knives, but that is a 



FIG. 218. SECTION RAZOR WITH HEAVY BLADE HAVING STRAIGHT BACK 



AND EDGE. 



great mistake, for the thin blade bends and vibrates in cutting firm 

 tissue and large pieces. There is no possible advantage in a thin- 

 bladed section knife for microtome work, but much disadvantage 

 from the lack of rigidity. (See the catalogues of microtomes and sec- 

 tion knives by the Bausch & Lomb Optical Co. and the Spencer 

 Lens Co.) 



606. Sharpening section knives; hones and strops. Perhaps 

 it should be taken for granted that any one would appreciate the 

 impossibility of making good sections with a dull section knife, but 

 experience teaches the contrary. Students are prone to believe that 

 with one of the elaborate automatic microtomes, good sections may 

 be made with any kind of an edge on the knife. It is forgotten that 

 the knife is the most important part; all the other mechanism is simply 

 its servant. 



For sharpening, select a fine yellow Belgian hone, and a very fine 

 Arkansas hone. As a rule hones from the factory are not sufficiently 



