REAGENTS. 805 



remove air-bubbles, and a warm coverglass applied, care being 

 taken to prevent the formation of air-bubbles. Evaporation of the 

 glycerin jelly is prevented by the use of shellac cements, asphalt 

 varnish or candlewax. 



The following method may be used for the preparation of 

 Canada balsam mounts : The specimen is cleared, dehydrated 

 by the use of alcohol and then placed in chloroform or benzol. 

 The clearing of the specimen is materially assisted by placing it 

 in oil of cloves or turpentine prior to mounting it. A drop of 

 Canada balsam solution ( i part of balsam to 3 parts of chloroform 

 or benzol) is placed on a slide and the specimen mounted. When 

 the preparation is nearly dry, scrape off the excess of balsam, 

 clean the sHde and coverglass with chloroform or benzol, and 

 ring with cement. 



Dried Material. — Most of the vegetable drugs and some of 

 the vegetable foods occur in commerce in a more or less dried 

 condition, a.id in order to study them microscopically it is usually 

 necessary to give them some preliminary treatment. With the 

 majority of drugs, soaking in hot or cold water for from a few 

 minutes to a few hours will render them sufficiently pliable or soft 

 for sectioning. After this the material is hardened by placing it 

 in alcohol (60 to 70 per cent.) for a few hours or over night. 

 It may then be sectioned and treated with special reagents or 

 stains as desired. 



