36 Botanical Microtechnique 



If a mixture ot two solvents is used, the bottle should be kept 

 corked until the infiltration is well advanced, to prevent the differen- 

 tial c\'aporation of the two solvents in the oven. 



Pour a teaspoonful of melted paraffin over the cold solvent, where 

 the paraffin solidifies as a layer on toji of the solvent. Remove the 

 stopper and place the bottle into the 35°C. oven. The layer of }Kiraf- 

 fin does not melt, but ii gradually dissolves and diffuses downward 

 into the tissues. If all of the paraffin dissolves at this temperature, add 

 more melted wax. If the bottle becomes filled with solution, pour 

 some of the solution into the waste can (not into the siuk!) . Con- 

 tinue the addition of melted wax until a thin layer of undissolved 

 wax remains on top of the solution. The undersurface of the layer of 

 paraffin eventually develops a translucent, crystalline appearance. 

 When this stage is reached, the solvent is obviously saturated with 

 paraffin at this temperature. Tissues are not damaged by prolonging 

 this infiltration at 35°C., therefore, this part of the process may be 

 extended over 2 or 3 days. 



Transfer the specimen bottle to the 53 °C. oven, where the layer 

 of solidified paraffin soon melts and continues to dissolve, and the 

 infiltration initiated at the lower temperature is contintied. If the 

 specific gravity of the solvent has not been adjusted as described 

 above, it is best to remove the solid supernatant wax at this point 

 and add wax by small increments at intervals as described later. 



If the tissues are not extremely delicate or fragile, whirl the bottle 

 genlly until the liquid is homogeneous, as shown by the absence of 

 refraction waves within the liquid. At intervals of 1 to 4 hr., pour off 

 one-half of the homogenized solution into the waste can. Replace the 

 decanted licjuid with an ecjual volume of melted soft paraffin, and 

 replace the bottle into the oven quickly. After four or more such 

 partial rej^lacements, poiu' off all the paraffin-xylene solution, ^\•hich 

 now consists mostly of j)araffin. and rej^lace with pure paraffin. After 

 1 to 4 hr. make another complete replacement and make a hultoti 

 test. Cast a button of paraffin about the size of a siher dollar b\ jxjur- 

 ing some of the paraMm irom the tissues into a pan of cold water. 

 Promptly replace the sjjecimen bottle into ilie oven. Allow the test 

 disk to cool thorouglih. Tlie cooled test button should not be greasy. 

 Chew a piece of this paraffin. The jjresence of e\en a slight trace 

 of xylene or other solvent is easily detected by taste. Examine for the 

 paraHin or connnercial casting comj)oinid at 1- to 4-hr. intervals. The 

 defects and cjualities described on page 31. If the test j)iece indicates 

 that all the solvent has Ijeen remoNcd, make two changes of hard 

 material is then ready to be cast into a mold. 



