156 GENERAL BIOLOGY 



directions for its purchase. Denatured alcohol may be 

 used and is cheaper, and about as satisfactory, as the regular 

 alcohol. Grain or ethyl, and not wood or methyl alcohol, 

 should be used ; the latter is poisonous. 



Commercial alcohol is ordinarily about 95 per cent in 

 strength. To make various grades from the commercial 

 product, fill a graduate with 95 per cent to the mark which 

 indicates the desired strength, and then add water up to 

 95 cc (e. g., to make 70 per cent from 95 per cent take 70 

 cc of alcohol and add water up to 95 cc) . It is well to have 

 alcohol of the following grades prepared: 35 per cent, 50 

 per cent, 70 per cent, 80' per cent, 95 per cent. These will 

 be used in the preparation of slides. For preservation 70 

 per cent or 80 per cent is used. 



Acid Alcohol. Of 70 per cent alcohol take 99 cc and of 

 concentrated hydrochloric acid Ice. Used chiefly for 

 destaining tissues. 



Anilin Dyes. For staining, these may be dissolved in 

 water, or in alcohol of any grade. They, are most com- 

 monly used in aqueous solutions. It is better to stain for 

 some time with a weak solution, than for a brief period 

 with a strong mixture. Some of the stains will be removed 

 by alcohol, and experience, or reference to some book on 

 technic, must show the best methods of use. The com- 

 mon dyes used for the staining of the cytoplasm are: eosin, 

 congo-red, acid fuchsin, light green, orange G. 



Benedict's Solution. Used in the same way as Fehling's 

 solution for demonstrating the presence of grape sugar. 

 This solution is said not to deteriorate on long standing. 



Sodium citrate 173 g. 



Sodium carbonate 100 g. 



Dissolve in 600 cc water, using heat. Filter and make up 

 to 850 cc with water. Dissolve 17.3 g. of copper sulphate 



