PENETRATION OR CLEANING. 175 



CHAPTER XY. 



IMBEDDING METHODS PARAFFIN AND OTHER FUSION MASSES. 



275. Penetration or Clearing. The first stage of the paraffin 

 method consists in the penetration or infiltration of the 

 object by some substance which is a solvent of paraffin. The 

 process may be called a clearing process, since the chief 

 substances used for infiltration are also "clearing" agents. 



The process of penetration or clearing should be carefully 

 performed with well-dehydrated objects in the manner de- 

 scribed in a former chapter. 



Penetration liquids being merely liquids that are, on the 

 one hand, miscible with alcohol, and on the other hand good 

 solvents of paraffin, are as numerous as could be wished. 

 Amongst them may be mentioned essence of turpentine, clove 

 oil, bergamot oil, creasote, benzol, xylol, toluol, naphtha, oil 

 of cedar wood, chloroform, and anilin oil. 



Turpentine penetrates well and mixes readily with paraffin. 

 I do not, however, recommend it, because in my experience 

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

 to delicate structures. 



Clove oil penetrates well, and preserves delicate structures 

 well ; but it mixes very slowly with paraffin, and quickly 

 renders tissues brittle. 



Benzin has been recommended by BEASS (Zeit. f. wiss. 

 Mik., ii, 1885, p. 301). 



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

 Anz., 1885, p. 223). 



Naphtha has been recommended by WEBSTER (Journ. Anat. 

 and Physiol., xxv, 1891, p. 278). For large specimens it has 

 the advantage of being very cheap. Dr. Webster writes me 

 that a quality known as "Persian naphtha" is best for fine 

 work, but the common pure naphtha is sufficient for ordinary 

 work. 



Xylol is said by HEIDENHAIN (see Zeit. f. wiss. Mik., ix, 2, 



