4 6 
capable of being scratched with a pin, and as a lubricant 
water or filtered kerosene oil may be used. If the 
razor is hollow-ground on one side only, it should be 
honed only on this side. After honing, the razor 
should be stropped. On one side of the strop a 
minimum amount of razor paste should be rubbed in 
and the leather side should be kept scrupulously clean 
and dry. 
» Examined under the microscope the edge should 
now present a clear, sharp line. It may be tested on 
a thin hair, which it should easily cut. 
Clearing. —I. Dehydrate the tissue by placing 
in quite water-free absolute alcohol. This is prepared 
in the following way : Heat copper sulphate crystals 
in a basin until all trace of blue is gone. Cool and 
add to the alcohol in the bottle. 
2. Pour some ordinary* cedar-wood oil into a 
specimen tube. (Or the tissue when dehydrated 
may be placed in a tube of xylol or chloroform or other 
clearing agent until quite transparent.) Pour on top 
of this some water-free absolute alcohol. 
3. Place the tissue in ; it floats at the junction 
layer of the alcohol and the oil. 
4. Allow to remain until it sinks into the oil. It 
is then ready for transferring to paraffin. 
Choice of Paraffin —For the most delicate work, 
a paraffin with a low melting point (45 0 ) is necessary, 
but in the tropics a much harder paraffin is necessary, 
e.g ., one melting about 6o°C. Superheated paraffin 
(Count Spee’s), melting about 56°, gives excellent 
ribbons, when the room temperature is low enough to 
allow of its use. 
P0 Embed Pissues. —1. The tissue, now transparent, 
* Not immersion oil. 
