46 Animal Micrology 



DIFFICULTIES LIKELY TO BE ENCOUNTERED IN SECTIONING IN 

 PARAFFIN, AND THE PROBABLE REMEDY 



1. Crooked Ribbons. a) Usually caused by wedge-shaped sections. 

 Correct by trimming the block of paraffin so that the edge which strikes 

 the knife first and the edge on the opposite side are strictly parallel. 

 See that the block strikes the knife exactly at right angles. 



b) The paraffin may be softer at one end of the block than at the 

 other. This can only be corrected by imbedding the object over again 

 in a homogeneous paraffin. 



2. The Object Makes a Scratching Noise on the Knife or Cuts with a Gritty 

 Feeling and the sections perhaps crumble and tear out from the paraffin. 



a) This is generally caused by too high heating of the object while 

 in the paraffin oven. Not only is such an object worthless but it endan- 

 gers the edge of the microtome knife. Correct by limiting the bath in 

 paraffin to the minimum time necessary for a proper penetration of the 

 object, and keeping the temperature barely above the melting-point of 

 the paraffin. 



6) The fixing reagent has formed crystals (e.g., corrosive sublimate) 

 which have not been thoroughly washed out. 



See also 5. 



3. The Sections Wrinkle or Jam Together; the object itself may be com- 

 pressed before the knife. This is a serious fault because the arrange- 

 ment of the parts of a tissue are greatly deranged. It may be due to 

 various causes. 



a) The microtome knife may be dull. Examine the knife and sharpen 

 it if necessary. 



6) The paraffin may be too soft. To remedy this defect employ one 

 or more of the following means: (1) cool the paraffin block in water; 

 (2) cut the sections in a cooler room; (3) cut the sections thicker; (4) re- 

 imbed in harder paraffin. If sections are not too badly wrinkled they 

 may be flattened out by warming on water as directed in steps 18-20. 



c) A possible reason is that the tilt of the knife is insufficient (see 

 step 12). 



d) The edge of the knife may be smeared with a layer of paraffin. 

 Clean the edge with a cloth moistened in xylol. 



4. The Sections Roll and Refuse to Ribbon. This is one- of the most 

 exasperating of all defects. If the sections are not tightly curled 

 they frequently unroll when placed on warm water (step 18). Various 

 mechanical devices have been constructed to prevent this evil, but most 

 of them are impractical. Sometimes when a section begins to roll, if the 

 edge is held down by means of a flat-pointed hair brush, the curling can 

 be overcome. If a ribbon can once be started the difficulty is frequently 

 corrected. The sections should be cut rapidly. 



