26 HISTOLOGY OF MEDICINAL PLANTS 



ture, and general arrangement or plan or structure if a section 

 of a plant, or, if a powder, to note its striking characters. All 

 the finer details of structure are best brought out with the 

 high-power objective in position. 



In placing the high-power objective in position, it is first 

 necessary to raise the body by the coarse adjustment; then 

 open the iris diaphragm, and lower the body until the objective 

 is within about one-eighth of an inch of the slide. Now raise 

 the tube by the fine adjustment until the object is in focus, 

 then gradually close the iris diaphragm until a clear definition 

 of the object is obtained. Now proceed to make an accurate 

 sketch of the object or objects being studied. 



In using the water pr oil-immersion objectives it is first 

 necessary to place a drop of distilled water or oil, as the case 

 may be, immediately over the specimen, then lower the body 

 by the coarse adjustment until the lens of the objective touches 

 the water or the oil. Raise the tube, regulate the light by the 

 iris diaphragm, and proceed as if the high-power objectives were 

 in position. 



The water or oil should be removed from the obiectives and 

 from the slide when not in use. 



After the higher-powered objective has been used, the body 

 should be raised, and the low-power objective placed in position. 

 If the draw-tube has been drawn out during the examination 

 of the object, replace it, but be sure to hold one hand on the 

 nose-piece so as to prevent scratching the objective and Abbe 

 condenser by their coming in forceful contact. Lastly, clean 

 the mirror with a soft piece of linen. In returning the micro- 

 scope to its case, or to the shelf, grasp the limb, or the pillar, 

 firmly and carry as nearly vertical as possible in order not to 

 dislodge the eye-piece. 



ILLUMINATION 



The illumination for microscopic work may be from natural 

 or artificial sources. 



It has been generally supposed that jthe best possible illumi- 

 nation for microscopic work is diffused sunlight obtained from 

 a northern direction. No matter from what direction diffused 



