142 IMBEDDING METHODS. 



The celloidin method and the remaining methods will form 

 the subject of the next chapter. 



268. 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 011 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, 

 creasote, benzol, xylol, toluol, oil of cedar wood, and chloroform. 



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 recently recommended by BRASS (Zeit. f. 

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



Toluol (or toluen) has been recently recommended by HOLL 

 (Zool. Anz., 1885, p. 223). 



Chloroform mixes well with paraffin, and after evaporation 

 in a paraffin bath (in the manner described in the next para- 

 graph) leaves behind a pure and very homogeneous paraffin, 

 having but little tendency to crystallise. But it is deficient 

 iu 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. 

 Chloroform ought therefore to be reserved for small and easily 

 penetrable objects. 



Cedar-wood oil is, according to my continued experience, 

 for the reasons stated by rne in Zool. Anz. t 1885, p. 563, in 

 general the best clearing agent for paraffin imbi'ddino-. It 



