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 
