CHAPTER IX 



IMBEDDING METHODS PARAFFIN AND OTHER FUSION 



MASSES 



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

 method consists in the saturation of the object with some sub- 

 stance wliich 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 § 155. 



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. 



As a general thesis the best of all these are benzol or carbon bisulphide 

 chloroform {for small objects), methyl benzoate-benzol and cedar oil. 



Turpentine we do not recommend, because in our experience 

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

 delicate structures. 



Clove oil mixes very imperfectly with j)araffin, 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 nmch used. 



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

 1885, p. 223). 



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 bath, or by successive baths of paraffin, as if the least 

 trace of it remains in the paraffin used for cutting it will make 

 it soft. The process of removal requires a very long time, in 

 some cases days. It ought therefore to be reserved for small 

 and easily penetrable objects. 



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