PREPARATION OP SPECIMENS 17 



in melted paraffin the specimen may be preserved 

 for future reference. Paper or metal molds are pre- 

 pared as directed in the section on Infiltration. The 

 paraffin should have a melting point not higher than 

 60° C. A layer of paraffin is poured into the mold 

 and cooled, the surface of the specimen is dried, after 

 which it is dipped into the melted paraffin and placed 

 in proper position upon the layer of paraffin already 

 in the mold. Melted paraffin is now poured into the 

 mold so as to cover the specimen, enough being added 

 to form a substantial layer over the latter. It must 

 be borne in mind that paraffin undergoes consider- 

 able contraction upon cooling. After the paraffin is 

 thoroughly hardened the mold is removed and the 

 block trimmed to convenient size. Sections may be 

 cut by hand or by machine according to the methods 

 outlined in the section on Infiltrated Materials. The 

 removal of paraffin from the specimens is readily 

 accomplished by placing the sections with the adher- 

 ing paraffin in a beaker, adding water and gently 

 heating. With most specimens a complete separation 

 is thus effected, as, upon cooling, the paraffin accumu- 

 lates on the surface of the water and the sections re- 

 main at the bottom. 



SYNOPSIS OF SECTIONING METHODS 



Infiltration Method: 



1. Fixing and hardening. 



2. Washing to remove fixing agent. 



(a) Staining may be desirable at this point. 



3. Dehydration. 



4. Clearing. 



5. Infiltration. 



6. Embedding. 



