8 
PHARMACEUTICAL BOTANY 
2. Never allow the objective to touch the cover glass or the liquid 
in which the object is mounted. 
3. Note whether the front lens of the objective is clean before 
attempting to use it. If soiled, breathe on the lens and gently wipe 
with an old, clean, soft handkerchief or lens paper. If the lens be 
soiled with balsam or some other sticky substance, moisten the 
handkerchief or lens paper with a drop of xylol, taking care to wipe 
it perfectly dry as soon as possible. 
4. Do not let the objective remain long near corrosive liquids, 
such as strong solutions of iodine, corrosive sublimate, or mineral 
acids. Never examine objects lying in such fluids without putting 
on a cover glass. 
5. Never lift the slide from the stage, but, after raising the objec- 
tive, slide it off the stage without upward movement. 
6. Never allow the stand (microscope without lenses) to be wetted 
with such substances as alcohol, soap, etc., which dissolve lacquer. 
7. Keep the microscope covered when not in use. 
THE TECHNIQUE OF MAKING PERMANENT MOUNTS 
1. 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 (acetic acid, formaldehyde) 
to the water used in mounting and carefully sealing the cover glass. 
As a rule, a better way is to use a mounting medium that will not 
evaporate, e.g., glycerine or Canada balsam. Both 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. Canada balsam, 
on the other hand, slowly becomes solid, so that the mount is ex- 
posed to no accident short of actual breakage. Balsam has the dis- 
advantage of being non-miscible with water, so that before it can 
be used the object must be carefully dehydrated. Even after this 
is done, and the object lying in absolute alcohol, an oil must be used 
as an intermediate agent between alcohol and balsam. 
