460 ZOOLOGY. 



revenue of the district in which the school is located. Applica- 

 tion should be made several months before the alcohol is 

 needed. 



Formaldehyde has been much used in recent years as a sub- 

 stitute for alcohol, or in combination with it, as a preservative. 

 It may be obtained as a 40 per cent, solution, and be further 

 reduced by adding from 10 to 20 times its volume of water. 

 This gives in the neighborhood of 4 per cent, to 2 per cent, 

 solution and the resulting fluid will safely preserve materials 

 through the term. The same care must be observed as with 

 alcohol. If the formol affects the pupils unpleasantly, the 

 specimens may be washed in water before studying. 



Killing Reagents. Chloroform is usually used as a stupe- 

 fying reagent. Air-breathing animals exposed to its fumes are 

 soon rendered unconscious, and die in a relaxed condition. 



Minute water animals as Hydra, Dero, and the like, are 

 often advantageously killed by sudden immersion in hot water 

 or hot corrosive sublimate (saturated solution). 



Staining Reagents. A few stains are of advantage, if there 

 is any attempt to study tissues or the Protozoa. 



Magenta (aqueous solution). One part by weight of the 

 dry magenta or fuchsin in 100 parts of water. Stains 

 fresh tissues well, but is not a nuclear stain. 



Methyl green; one per cent, aqueous solution. Add one part 

 of acetic acid to 100 parts of this. The resulting fluid 

 is a superior nuclear stain for elementary work. 



Mounting Reagents. Water, alcohol of different strengths, 

 glycerine, and normal salt solution (% P er cent - solution of 

 common salt) are the more commonly used materials for tem- 

 porary mounting of objects to be examined under the micro- 

 scope. The normal salt solution is especially valuable for 

 delicate fresh tissues, blood, and the like. The teacher must 

 consult works on microscopical methods for information about 

 the making of permanent mounts. 



Beside the materials mentioned above it is often desirable to 

 have other substances, as sugar, acids, salts, and some of the 



