158 GENERAL BIOLOGY 



Fehling's Solution. 



A. Copper sulphate 34.65 g. dissolved in ... 500 cc of water 



B. Sodium or potassium hydroxide .... 125 g. 

 Sodio-potassium tartrate (Rochelle salts) . 173 g. 



Dissolve in 500 cc of water. 



Keep solutions separate until ready to use. Just before 

 using mix equal parts of A and B. This solution is used to 

 test for the presence of grape sugar. 



Formalin. Commercial formalin is a solution of formalde- 

 hyde gas in water (40 per cent). To use, this is considered 

 as absolute and a 5 or 10 per cent solution made (e. g., to 

 make 5 per cent formalin mix 5 cc of commercial formalin 

 and 95 cc of water). For practically all organisms, plant 

 and animal, used in the laboratory or in the museum 5 per- 

 cent formalin is an efficient preservative and for most things 

 as satisfactory as alcohol. If the tissues are very watery 

 the solution should be changed after twenty-four hours. 



Glycerin. Use pure or diluted with equal parts of water 

 or alcohol. Useful as a clearing agent and as a temporary 

 mounting medium. 



Hematoxylin (Delafield's). Hematoxylin crystals 1 g. di,s- 

 solved in 10 cc of strong alcohol. Add this slowly to 100 cc 

 of saturated aqueous solution of ammonium alum, stirring. 

 Expose this solution to the air for several weeks to ripen. 

 Filter and add 25 cc of glycerin and 25 cc of methyl 

 alcohol. 



Hematoxylin is one of the most satisfactory stains for 

 tissues; it is a nuclear stain. To use, dilute the stain and 

 let it act until the tissue is dark and overstained. Destain 

 with acid alcohol or with very dilute aqueous hydrochloric 

 acid (1 per cent of acid or less, in water). The slides hold- 

 ing the sections must now be washed for at least five minutes 

 in running water, to remove the acid and restore the blue 



