46 



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) is necessary, 

 but in the tropics a much harder paraffin is necessary, 

 e.g., one melting about 6oC. Superheated paraffin 

 (Count Spec's), melting about 56, gives excellent 

 ribbons, when the room temperature is low enough to 

 allow of its use. 



To Embed Tissues. I . The tissue, now transparent, 



* Not immersion oil. 



