FIXING MATERIAL FOR CUTTING. 185 



with some firm substance and not merely embedded 

 therein. Two embedding materials are in general 

 use paraffin and celloidin. The latter will not be 

 described, as it is only necessary for special work and 

 for ordinary purposes cannot compare with paraffin for 

 beauty of results and facility of application. 



In the paraffin process the tissue is infiltrated through- 

 out with hard paraffin (such as is used for the better 

 varieties of paraffin candles) so that every cell and every 

 fibre is permeated and supported on every side. To do 

 this requires a number of processes. It would be of no 

 use to immerse the block of tissue in the paraffin just as 

 it is, for the paraffin would not wet it, much less soak 

 into it. The water is first removed ; and this is done 

 by soaking the material in absolute alcohol. But 

 alcohol does not dissolve or mix with paraffin ; it is 

 therefore necessary to remove it by means of some fluid 

 which will mix with it on the one hand and paraffin on 

 the other. Of these there are many ; xylol, chloroform, 

 benzine, cedar oil, and many more are in use for special 

 purposes. Chloroform answers most purposes and is to 

 be generally recommended. The block of tissue is now 

 ready to be soaked in melted paraffin ; it is kept in a 

 bath of this substance until the chloroform has been 

 entirely driven off and replaced by the paraffin. The 

 whole is then allowed to cool, is shaped into suitable 

 blocks, and is then ready for cutting. 



We shall now describe the processes in fuller detail. 



FIXING MATERIAL FOR CUTTING. 



These processes must be understood by all practi- 

 tioners, even although they do not intend to cut sections 



