356 REAGENTS AND THEIR PREPARATION [Ch. X 



a saturated solution of alcoholic eosin is made. This is also used for 

 staining with methylene blue (§ 564). 



§564. Eosin-Methylene blue. — Alcohol-soluble eosin, 3 grams; 

 95 c ' c alcohol, 500 cc. Methylene blue, pure, 2 grams; 95% alcohol 

 50 cc. ; distilled water 450 cc. 1 % aqueous solution of caustic 

 potash, 5 cc. 



For staining with this, material hardened in a mercuric mixture 

 is best. Stain sections or smears 1 to 5 minutes in the eosin. Rinse 

 well in water. Stain 1 to 5 minutes in the methylene blue solution. 

 Rinse well in tap water. Dehydrate quickly with absolute alcohol. 

 Clear in pure xylene and mount in neutral balsam (§ 546). 



§ 565. Ether, ether-alcohol. — Sulphuric ether (C 2 H 5 ) 2 is meant 

 when ether is mentioned in this book. Wherever ether-alcohol is 

 mentioned it means a mixture of equal volumes of sulphuric ether 

 and 95 % or absolute alcohol, unless otherwise stated. 



§566. Farrant's solution. — Take 25 grams of clean, dry gum 

 arabic, 25 cc. of a saturated aqueous solution of arsenious acid, 

 25 cc. of glycerin. The gum arabic is soaked for several days in the 

 arsenic water, then the glycerin is added and carefully mixed with 

 the dissolved or softened gum arabic. 



This medium retains air bubbles with great tenacity. It is much 

 easier to avoid than to get rid of them in mounting. 



§ 567. Flemming's Fluid. — Water 19 cc; 1% osmic acid 10 cc; 

 10% chromic acid 3 cc; glacial acetic acid 2 cc. This osmic fixer 

 is good for very small pieces — 1 to 5 millimeter pieces, thickness not 

 over 2 to 3 mm. Wash out with water 10 to 24 hours. Then 67 % 

 alcohol. Also 82 % and 95 %. 



§568. Formaldehyde (HCHO or OCH 2 ). — This is found in 

 the market under the name of "formalin," etc., and consists of a 

 40 % solution of formaldehyde gas in water. 



For fixing tissues and embryos a 5 % solution is good (formalin 

 1 cc, water 7 cc, § 537). A common fixer is 10 cc. formalin, 90 cc. 

 water. This is frequently called 10% formalin; it is, however, only 

 4% formaldehyde. 



Tissues may stay in this indefinitely. Small pieces are fixed 

 within an hour. Before hardening in alcohol and imbedding, wash 



