1 66 PRACTICAL PHOTO-MICROGRAPHY. 
solvent; if this is due to air in the tissue the latter may 
be pushed down into the liquids, and held there by a 
plug of wool; if due to the specific gravity of the 
tissues, ether may be added to the chloroform till the 
tissue sinks. It is important to adjust the melting- 
point of the paraffin to the temperature at which the 
sections are to be cut. In winter, or for a cold room, 
the melting-point may be about 46° to 48° C. ; in 
summer, or a warm room, 52 0 or even 56° C. may be 
advisable. This is a matter for experiment and of 
experience ; no rule can be laid down. 
If the paraffin is too soft, the sections will be folded 
and wrinkled when cut; if too hard, they will come off 
the knife in rolls like tiny pencils. We have never 
known tissues spoiled by the heat needed for paraffin 
process if the fixation and hardening of the tissue had 
been properly carried out. But the principle to follow 
is to use as soft paraffin as will allow good sections 
to be cut, or to make the room where they are cut as 
cold, within limits, as possible. By far the most con¬ 
venient and trustworthy stoves, or incubators, known 
to us are those of Idearson. We have used several for 
years, and have never had the slightest hitch with 
them. When not in use they are turned out, and no 
readjustment is required when they are relighted_this 
touches the gas stoves only ; we have no experience 
of the others. The paraffin stove should run about 
4 0 or 5 0 Fahr. above the m.p. of the paraffin. The 
impregnation by paraffin may be conducted in small 
dishes known as “ Cheese-Ramequin dishes,” and in 
