Chapter V: The Paraffin Method 45 



drawn lightly across the ball of the thumb, freely enters the moist epi- 

 dermis. Finally the blade is wiped clean with a soft cloth, great care 

 being taken not to injure the edge. 



Stropping. A broad firm strop of finest calfskin is best. It should 

 be affixed to a solid back so that it will not spring and thus round off the 

 delicate edge of the knife. 



In stropping, the motions are the same as in honing (both sides of 

 blade), only the knife passes back foremost and from heel to point. The 

 blade must move lightly over the surface of the strop with very slight 

 pressure on the part of the operator. The stropping is ordinarily consid- 

 ered sufficient when the blade will cut a loose hair freely along every part 

 of the edge. An examination under a low power of the microscope should 

 reveal no nicks in the edge. 



12. To Remove Pigments and to Bleach Osmic and Chromic Acid Materials 

 a 3 per cent, solution of peroxide of hydrogen frequently is sufficient. 

 Tissues left too long in this liquid macerate. 



Mayer's chlorine method is one of the best for bleaching. To several 

 crystals of chlorate of potash in a glass tube a few drops of hydrochloric 

 acid is added. When the greenish fumes of chlorine appear, add from 5 

 to 10 c.c. of 50 per cent, alcohol. The 

 object, which in the meantime has been 

 standing in 70 per cent, alcohol, is 

 transferred to the tube. From 15 min- 

 utes to 24 hours are required for bleach- 

 ing, depending upon the nature of the 

 material. It is well to suspend the ob- 

 ject from the mouth of the bottle. Sec- 

 tions on the slide may be bleached in a imd 1 Ls f r molding 

 few minutes. This method is especially 

 recommended for removing natural pigments and for bleaching osmic 

 material. 



13. Large Objects May Be Cut in Paraffin better with a slanting knife 

 than with a square-set one. The block of paraffin must be trimmed 

 to a three- sided prism with its most acute angle farthest from the object. 

 A sliding microtome is used ordinarily and the block of paraffin is so 

 oriented that the knife enters at the sharpest angle of the prism. Each 

 section as cut is removed with a brush. 



14. Metal "Ls" Are Frequently Used Instead of Paper Boxes for mold- 

 ing paraffin blocks. The two Ls (Fig. 30) may be placed together 

 on a small glass or metal plate in such a way as to mold blocks of any 

 desired size. Before pouring the melted paraffin in, the inner walls of 

 the metal pieces should be lightly smeared with glycerin so that the 

 block of paraffin will easily separate from them when cool. 



