20 PHARMACEUTICAL BOTANY 



signed for a cord or strap when it is desired to run the instrument 

 by a motor. 



THE TECHNIQUE OF MAKING A TEMPORARY MOUNT 



1. Place a drop or two of water (or reagent) in the center of a clean 

 glass slide. 



2. With the aid of a forceps take the section or very small quantity 

 of the material to be examined and spread it on the drop of water. 



3. Place a clean cover-glass over the material. In placing the 

 cover-glass do not drop it flat upon the drop of water, but place one 

 side of it down first and allow it to squeeze the water along under it. 



4. Keep the top of the cover-glass dry. 



When filamentous algae or molds are to be examined, the material 

 tends to cling together and must be carefully separated, in the drop 

 of water, with dissection needles before the cover glass is placed over 

 the material. In case a coarse ground drug is to be mounted the 

 coarser particles should be first crushed in the water on the slide 

 and subsequently teased apart with dissection needles. 



Care should always be taken to see that the water or mounting 

 medium used is not contaminated with foreign substances. This 

 can best be practiced by examining the mounting medium under the 

 microscope before the material to be examined is placed in it. 



THE TECHNIQUE OF MAKING PERMANENT MOUNTS 



i. The Mounting Medium. When a microscopic object is to be 

 preserved permanently it must be kept from decaying and the fluid 

 in which it is placed must be kept from evaporating. These condi- 

 tions can be met by adding an antiseptic (2 per cent, acetic acid, or 

 formaldehyde) to the water used in mounting and carefully sealing 

 the cover glass with asphaltum or zinc white. As a rule, a better 

 way is to use a mounting medium that will not evaporate, e.g., 

 glycerine, glycerin gelatin or Canada balsam. These fluids have 

 a high refractive index and so render the objects penetrated by them 

 more transparent. This quality is generally an advantage, but for 

 objects already almost transparent it is quite the reverse. Glycerine 

 has the disadvantage of always remaining soft, so that the mount 

 may at any time be spoiled by careless handling. "Glycerin-gelatin 



