138 



THE FROG 



CHAP. 



lutely necessary step in order that they may be permeated 

 with paraffin. 



d. Imbedding. Transfer the objects from absolute 

 alcohol to turpentine or xylol. Either of these fluids acts 

 as an intermediary between alcohol and paraffin, being 

 freely miscible with both : it gradually replaces the alcohol 

 in the tissues, rendering them transparent. If they are not 

 transparent in the course of an hour or so, the process of 

 dehydration has not been complete, and they must be 

 returned to absolute alcohol. In the meantime, melt some 

 paraffin over the water-bath, using various mixtures of hard 

 and soft according to the season : in a cold room in winter 



soft paraffin will be hard 

 enough ; in the height of 

 summer hard paraffin alone 

 will be suitable. The tem- 

 perature of the water-bath 

 must never be allowed to 

 rise more than a degree or 

 two above the melting- 

 point of the paraffin. 

 Transfer the objects from 

 turpentine or xylol to 

 melted paraffin and keep 

 them in it for some hours 

 the time varies according 

 to the size of the piece 



FIG. 43-A, imbedding box made by wrap- until the Y are thoroughly 



ping paper round a cork ; B, cork after permeated . 



removal of the paper, showing the j f w iqh -j- n rir f- c Pr 



paraffin pared down to a convenient - 1 y ou wlsn to ( 



size for sectioning, a, object to be tions by hand, get Some 



cut - ordinary medium - sized 



bottle-corks : around each 



wind a piece of paper, allowing it to project about J an 

 inch beyond one end of the cork, and fixing it with a pin, 

 as in Fig. 43, A. Into the little cylindrical vessel or 

 imbedding box thus formed pour some melted paraffin, and 

 immediately transfer to it, by means of a warmed section- 

 lifter or forceps, one of the prepared pieces, adjusting its 

 position by means of a heated needle. When the paraffin 

 is quite cold remove the paper, and you will have fixed to 

 the cork a solid block of paraffin containing the object to be 

 cut. 



e. Section-cutting. Pare away the block of paraffin until 

 the object comes into view : then trim the block, as in- 

 Fig. 43, B, until its upper surface, with the object in the 



