REAGENTS. 



Certain stains and reagents are absolutely indispensable for 

 laboratory work while others although not indispensable are never- 

 theless very desirable and become necessary in thorough and 

 advanced investigations. The following is an alphabetical list of 

 the more important chemicals, reagents, and stains, together with 

 tests for the more frequently occurring vegetable substances. 



Alcohol. 



For all ordinary laboratory manipulations commercial 95 per 

 cent. Ethyl alcohol is sufficiently strong, and it is only when all 

 trace of water is to be removed from a specimen, that alcohol of 

 absolute strength is needed. Absolute alcohol has like osmic acid 

 the property of rendering protoplasm rigid and can therefore be 

 employed to advantage in studying the more intricate structures 

 of protoplasmic bodies ; as for example, nucleus or cell division. 

 Common alcohol readily removes air from intercellular spaces, 

 especially if heat is applied. It is also extensively used in harden- 

 ing tissues, different strengths being employed to prevent its strong 

 avidity for water causing too great a shrinkage of the protoplasm 

 from the cell wall. Tissue hardened in this way can be softened 

 again by soaking it in water. Alcohol is used for dehydrating sec- 

 tions that are to be mounted in balsam and for dissolving many 

 fats, resins, and oils from plant tissues. 



It is a solvent for chlorophyll, and is used in the preparation 

 of many stains. If tissue containing inulin is kept in alcohol, the 

 inulin is precipitated within the cell in the form of sphaero-crys- 

 tals. Many sphaero-crystal forming substances separate in the 

 same way, e. g., hesperidin. 



