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 

 Abbe 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 Abbe 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 

 Abbe 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 



