28 HISTOLOGY OF MEDICINAL PLANTS 
illumination. The type of the screen used will be varied accord- 
ing to the nature of the object studied. 
CARE OF THE MICROSCOPE 
If possible, the microscope should be stored in a room of 
the same temperature as that in which it is to be used. In 
any case, avoid storing in a room that is cooler than the place 
of use, because when it is brought into a warmer room, moisture 
will condense on the ocular objectives and mirrors. 
Before beginning work remove all moisture, dust, etc., from 
the inner and outer lenses of the ocular, the objectives, the 
Abbé condenser, and the mirror by means of a piece of soft, 
old linen. When the work is finished the optical parts should 
be thoroughly cleaned. 
If reagents have been used, be sure that none has got on 
the objectives or the Abbé condenser. If any reagent has got 
on these parts, wash it off with water, and then dry them thor- 
oughly with.soft linen. 
The inner lenses of the eye-pieces and the under lens of the 
Abbé condenser should occasionally be cleaned. The mechani- 
cal parts of the stand should be cleaned if dust accumulates, and 
the movable surfaces should be oiled occasionally. Never 
attempt to make new combinations of the ocular or objective 
lenses, or transfer the objectives or ocular from one microscope 
to another, because the lenses of any given microscope form a 
perfect lens system, and this would not be the case if they were 
transferred. Keep clean cloths in a dust-proof box. Under no 
circumstances touch any of the optical parts with your fingers. 
PREPARATION OF SPECIMENS FOR CUTTING 
Most drug plants are supplied to pharmacists in a dried 
condition. It is necessary, therefore, to boil the drug in water, 
the time varying from a few minutes, in the case of thin leaves 
and herbs, up to a half hour if the drug is a thick root or woody 
stem. If a green (undried) drug is under examination, this 
first step is not necessary. 
If the specimen to be cut is a leaf, a flower-petal, or other 
