24 HISTOLOGICAL TECHNIC 



Care must be taken to have the filter paper several layers thick in 

 order that the oil may be completely removed. The specimen should 

 also be blotted firmly, giving the oil time to soak into the paper. 

 These two precautions are necessary to prevent the section adhering 

 to the paper instead of to the slide. After blotting, a drop of balsam 

 is placed upon the centre of the specimen and a cover-glass put on. 



When xylol is used, blotting is not necessary. Drain off the 

 excess of oil, put a drop of balsam on the specimen and put on a 

 cover-glass. 



Paraffin Sections. — The technic of staining and mounting paraffin 

 sections differs from that of celloidin sections. This is due mainly to 

 the fact that while cellodin is transparent and may remain perma- 

 nently in the specimen, paraffin is opaque and must be dissolved out 

 before the section is fit for microscopic study. 



Bulk staining with carmine (page 22) is frequently used for speci- 

 mens which are to be embedded in paraffin. Sections may be coun- 

 terstained if desired. 



The following are the steps to be followed in staining and mount- 

 ing paraffin sections: 



1. To attach sections to slide: 



Place a drop of egg albumen (equal parts white of egg and glycerin 

 to which a little carbolic acid may be added as a preservative) on a 

 slide, and spread it out thin with the finger. 



Place a few drops of distilled water on the slide. 



Float sections on the water. 



Warm gently to allow sections to flatten — must not melt 

 paraffin. 



Pour off excess of water, holding the ends of the ribbons to prevent 

 them floating off. 



Stand slides on end a few hours to allow water to evaporate. 



2. To remove paraffin: 



Place slide in xylol three to five minutes. 



3. To stain sections: 



Place slide in fresh xylol three minutes. 



Transfer to absolute alcohol. 



Transfer to gc-per-cent. alcohol. 



Transfer to 80-per-cent. alcohol. 



Transfer to 50-per-cent. alcohol. (May be omitted.) 



Transfer to water. 



Stain with an aqueous stain. 



