Infiltration and Embedding in Paraffin Wax 37 



The use of two, or even three grades of paraffin with different 

 mehing points, used successively during infiltration, has been sug- 

 gested in the literature. If a laboratory is ecjuipped with three ovens, 

 maintained at 40, 50 and 54°C., there may be some point to the 

 successive use of waxes having those melting points, but if the three 

 waxes are used at the same temperature, there seems to be little 

 basis for the procedure. It can be demonstrated easily that high- 

 melting-point wax that contains a trace of solvent becomes low- 

 melting-point wax. The progressive method outlined in this chapter 

 may be used with only one grade of wax; however, the use of inex- 

 pensive canning wax for preliminary infiltration, followed by casting 

 in a liigh grade filtered wax or compounded formula, is economical 

 and entirely satisfactory for most tasks. 



A vacuum oven is an aid in the infiltration of difficult material. 

 Cavities that resist evacuation at low temperature can be exhausted 

 at 50°C., when the material has progressed to approximately equal 

 volumes of wax and solvent. The low boiling point of tertiary butyl 

 alcohol makes the use of a vacuum oven impossible with this solvent 

 until the solvent has been almost completely replaced by wax. 



Most material can be adequately evacuated by the time it is in 

 the final solvent, and the dissolving wax will then diffuse into all 

 spaces occupied b) the solvent. 



CASTING INTO A MOLD 



Assume that the infiltrated material is in the final change of pure 

 paraffin. If the oven has cooled because of frequent opening, the 

 paraffin in the specimen bottle may have congealed. Heat the neck 

 and upper portions of the bottle in a Bunsen flame. Never heat the 

 bottom of the bottle because the tissues resting on the bottom will 

 be overheated and ruined. Apply only enough heat to liquefy the 

 paraffin. Slight heating repeated at 10-min. intervals is safer than 

 melting at one heating. If you have not yet provided means of 

 identification, write the designation of the given lot of material on 

 a y2-cm. square of paper and put into the bottle. Select a wax-soaked 

 paper boat that will accommodate the pieces in the specimen bottle, 

 without wasting space or wax. Heat one end of the casting plate with 

 a small flame and place the empty boat at the melting zone. Pour the 

 paraffin containing the tissues into the boat. Arrange the pieces with 

 a bristle. A warmed needle may be used, especially to move pieces 

 that have become frozen into unsatisfactory positions. Slide the boat 

 over the edge of the melting zone toward the cold end of the plate 

 as fast as a row of pieces is arranged. When the pieces are suitably 



