186 



PARAFFIN SECTIONING 



[CH. VII 



cools on the bottom, or a stratum of the paraffin may be cooled on the bottom 

 before putting the tissue in the box. Cool quickly after the tissue is in place. 



FIG. 156. Paraffin re- 

 ceptacle P, with water 

 bath and spout for par- 

 affin imbedding (i 88^ ) . 



\ 288. Cutting the Sections. After the imbedding mass is well cooled, re- 

 move the paper box and trim the end containing the tissue in a pyramidal form, 

 clamp the block of paraffin in the holder of the microtome so that the tissue will be 

 at the proper level for cutting. If a ribbon microtome is used, heat the holder and 

 melt the end of the block upon it. Cool and place the holder in its place in the 

 microtome. Use a very sharp, dry razor for cutting the sections. The sections 

 are made with a rapid, straight cut as in planing. Do not try to section with a 

 drawing cut as in collodion sectioning. If the temperature of the room is right 

 for the paraffin used, the sections will remain flat, and if the opposite sides of the 

 block are parallel, and one edge strikes the knife squarely, the sections will adhere 

 and thus make a ribbon. If the room is too cold for the paraffin the sections 

 will roll. If it is too warm the sections will crumple. 



Remember the sections must be very thin, from 3// to is// to show fine struc- 

 tural details to good advantage. 



The secret of making good ribbons of sections is to have the block of paraffin 

 containing the tissue cut square and properly arranged in the microtome so that 

 the block strikes the edge of the section knife at right angles with the edge ; and 

 finally the paraffin must be of a proper melting point for the room in which the 

 sections are to be cut. Remember that the larger the object the thicker must 

 be the sections, and the softer the paraffin. Frequently one may modify the tem- 

 perature if too cold by a Bunsen burner flame near the microtome. If it is too 

 warm one may go to a basement room. 



$ 289. Extending Sections with Warm Water. Paraffin sections are liable 

 to have fine wrinkles or folds in them. These folds are very annoying and often 

 obscure the structure. To get rid of them the sections are extended or stretched 

 upon warm water. One may put a ribbon of sections on warm water and then cut 

 the ribbon into pieces and transfer the pieces to slides. Practically, however, the 



