SECTIONING AND STAINING 653 



Much depends upon the choice and care of the knife. The 

 microtome knives of Jung are of excellent quality and should be 

 kept in good condition by the frequent use of the hone and strop. 



The hone should be of fine Belgian stone. It should be well 

 moistened with water, the addition of a little fine soap being a 

 distinct advantage. The edge of the knife, carefully applied to 

 the hone, should first be drawn obliquely from heel to toe and 

 toward the operator, being held at a constant angle and drawn the 

 whole length of the stone. The knife is then turned over and the 

 motion is reversed, the knife being held obliquely at an angle equal 

 to the previous one, the edge directed away from the operator, and 

 the knife pushed from heel to toe, the whole length of the stone. 

 The motion being repeated, a sharp edge is gradually acquired, 

 which can be finished by the use of the strop. 



In the use of the strop the motions are the reverse of those with 

 the hone, the back of the knife in this case preceding its edge as 

 it is drawn along the leather, and the draw should be from the 

 toe to heel of the knife. The angle, however, between the knife 

 and the hone and the knife and the strop should always be a con- 

 stant one, and should be such that the microscopical " teeth" 

 which are thus formed on the edge of the knife should be directed 

 obliquely toward its heel. 



In sectioning, the knife should be so placed in the microtome 

 that its edge crosses the parafin embedded object at right angles, 

 and for ribbon sectioning the parafin block should be so trimmed 

 that it forms a perfect rectangle. In sectioning celloidin embedded 

 objects, the knife should cross the object at as acute an angle as 

 possible. With parafin, also, the stroke should be sharp and quick ; 

 with celloidin, somewhat slower and rhythmic. The knife should 

 remain dry when used with parafin ; with celloidin both the knife 

 and the object should be at all times well moistened with 70 per 

 cent, alcohol. 



STAINING 



The sections, having been cut, are at once ready for staining, 

 provided they were embedded in celloidin. If parafin was used for 

 embedding, the sections have first to be fastened to the slide. This 

 is accomplished in the following manner. 



The parafin sections are properly arranged upon the surface of 

 a clean slide, a few drops of water from a pipette are allowed to 

 flow between the slide and the sections, so that the latter float upon 



