CARE OF SECTION KNIFE 



255 



way the edges of the sections adhere as they are cut and form a 

 ribbon which preserves the order of the series perfectly. In 

 cutting paraffin sections with the sliding microtome of the type 

 shown in Fig. 143 the knife needs to move through only a short 

 distance each way, so the elbow may rest u})on the table and the 

 knife may be operated with a wrist movement merely. 



Fig. 142. — Showing the manner of holding the knife blade on the glass ways, and, by the 

 arrow, the direction of sliding the knife while cutting the sections. 



Care of the Section Knife. — As has been said, and it will 

 bear repeating, the section knife or razor must be ke])t sharp— 

 what we call perfectly sharp, or as sharp as one can make it. 

 The test is that it should clip a hair at a slight touch. If it 

 will not do this it may need honing on a stone and then strop- 

 ping on leather, or the stropping may be all that it needs. To 

 tell what to do moisten the ball of the thumb and draw it lightly 

 over the edge of the knife from tip to heel; if the edge gives the 



