CHAPTER VIII. 



IMBEDDING METHODS PARAFFIN AND OTHER FUSION MASSES. 



138. Saturation with a Solvent. The first stage of the paraffin 

 method consists in the saturation of the object with some substance 

 which is a solvent of paraffin. The process is sometimes called 

 " clearing," since many of the substances used for infiltration are 

 also " clearing " agents. 



The process of saturation should be carefully performed with 

 well-dehydrated objects in the manner described in 119. 



Saturation liquids being liquids that are, on the one hand, miscible 

 with alcohol, and on the other hand good solvents of paraffin, are 

 not quite as numerous as could be wished. 



According to GRAEFE (Chem. Centralb., 1906, p. 874), at 20 C. 

 petroleum ether (1 c.c.) dissolves 200 mg. of paraffin, chloroform 

 246, benzol 285, carbon tetrachloride 317. And according to 

 APATHY, at 20 C. benzol dissolves 8 parts per cent., chloroform 10, 

 toluol 10, xylol 12, oil of turpentine 8, cedar oil 4 to 6, bergamot oil 

 0-5 to 3, creosote and clove oil hardly any. Acetone, according to 

 MAYER, dissolves hardly any. 



Turpentine I do not recommend, because in my experience it is 

 of all others the clearing agent that is the most hurtful to delicate 

 structures. 



Clove oil mixes very imperfectly with paraffin, and quickly 

 renders tissues brittle. 



Oil of bergamot mixes still more imperfectly with paraffin. 



Benzol has been recommended by BRASS (Zeit. wiss. Mik., ii, 

 1885, p. 301), and is now much used. 



Toluol (or toluen) has been recommended by HOLL (Zool. Anz., 

 1885, p. 223). 



Xylol is said by M. HEIDENHAIN (Kern, und Protoplasm, p. 114) 

 to be a cause of shrinkage in cells. So it is, if you use it to de- 

 alcoholise the specimens. But used after oil of cedar, or the like, it is 

 very good, as it is one of the best of solvents of paraffin. 



Chloroform is deficient in penetrating power, so that it requires an 

 excessive length of time for clearing objects of any size ; and it 

 must be very thoroughly got rid of by evaporation in the paraffin 



