MEDICAL AND BIOLOGICAL STAINING TECHNIQUES 



Stiff but easily deformable gel not altered in shape or size by 

 shrinkage; it should be considerably less hard than a Celloidin 

 block is usually made. 



7. Plunge the block into 75% alcohol. Change the alcohol 

 twice over a period of one to three days. 



8. Trim the block, removing the hard outer rim of the L.V.N. 

 Use 20% L.V.N, to mount it on the wood or fibre block. Harden- 

 ing is complete in a few minutes. Dip into 75% alcohol for a few 

 more minutes. 



Cutting sections: 



Cut the sections " dry ". If a Celloidin microtome is used the 

 tilt of knife should be the same as that used for cutting Celloidin, 

 but the angle the knife makes with the direction of travel should 

 be between 25° and 45° instead of the usual 75° used for Celloidin 

 sections ; this prevents the rolling of sections. 



Procedure for handling sections: 



1. Collect the sections in 75% alcohol; handle and stain as 

 usual. Dyes tend to stain L.V.N, less than Celloidin. 



2. Mount sections on to a slide from a bowl of 96% alcohol. 

 Flatten with tissue paper moistened with 96% alcohol ; press the 

 paper with a glass rod and then remove it. Repeat this several 

 times. 



3. Treat similarly several times with equal parts of absolute 

 alcohol and chloroform. 



4. Treat similarly several times with the solution C. 



5. Treat similarly several times with xylol. 



6. Mount in balsam. 



MERCURIC CHLORIDE PRECIPITATES IN SECTIONS: 



METHOD FOR REMOVAL 



Before proceeding to the staining of sections of tissues which 

 have been fixed in fluids containing mercuric chloride it is neces- 

 sary to carry out the following procedure, which is essential for 

 the removal of the deposits of mercuric chloride which would 

 obscure the picture. 



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