314 HISTOLOGICAL TECHNIQUE. 



Methods of Clearing. 



Clearing is necessary when specimens are to be permanently 

 mounted in Canada balsam or dammar. Its object is to impreg- 

 nate the section with some liquid that will drive out alcohol and 

 also be miscible with the resin used for mounting. Of these clear- 

 ing-agents there is a large number, from which a choice must be 

 made according to the method of embedding that has been employed 

 and the nature of the dve with which the tissues have been stained. 

 Clearing-agents also differ in their miscibility with water, some 

 requiring dehydration with absolute alcohol, others clearing well 

 when 95 per cent, alcohol has been used for dehydration. 



1. Xylol. — This is an excellent clearing-agent when the sections 

 have been well dehydrated with absolute alcohol. It does not 

 injure anilin-dyes. It is, perhaps, the best clearing-agent for 

 sections of tissue stained with borax-carmine before cutting, when 

 no counter-stain is employed. Xylol then both removes the paraffin 

 in the section and clears it. 



2. Carbol-xylol. — 



Carbolic acid crystals (melted), 1 vol. 



Xylol, 3 vols. 



This mixture is much more tolerant of water than pure xylol. 

 Sections dehydrated in 95 per cent, alcohol may be cleared with 

 this reagent, which does not dissolve collodion. The carbolic acid 

 used should be pure, but need not be the more expensive synthetic 

 product. 



3. Oil of Bergamot. — This light-green essential oil clears well and 

 does not dissolve collodion. It may be used when 95 per cent, 

 alcohol has been employed for dehydrating. 



4. Oil of Origanum. — The oleum origani cretici should be used. 

 It is of light-brown color and clears sections dehydrated in 95 per 

 cent, alcohol or stronger. It slowly discharges anilin-colors. 



5. Oil of Cloves. — This clearing-agent dissolves collodion and 

 discharges anilin-colors. It may be used when it is desired to get 

 rid of the collodion used for embedding after the sections have been 

 stained. This removal is favored by dehydration in absolute alcohol 

 before clearing. 



6. Oil of Cedar-wood. — This, when pure, has a very light-yellow 

 color and smells like cedar-wood. It should be free from the more 



