16 TREATMENT OF THE SUBJECT-MATTER. 
VI. Description of the drug itself according to external 
characteristics, the odor and taste, and, in the case of liquids 
also the spevific gravity. Drugs provided with organic struc 
ture present many more points of observation for their exami- 
nation and description. 
VII. The determination of the parts which here come under 
consideration, according to their organological importance. 
The general considerations relating to this subject are treated 
of in a subsequent morphological section. 
VIII. Microscopic structure of the drugs of organic con- 
struction. 
To this subject special sections of the present work are dedi- 
cated. Among those drugs in which development does not 
proceed from the activity of cell formation in the organism, or 
is not regulated in accordance with morphological laws, there 
are some (as for example: Aloe, Balsamum tolutanum, Benzo- 
imum, Catechu, Ohrysarobinum, Elemi, Opium, Styrax, and 
Terebinthina communis) which, nevertheless, with reference to 
their crystalline constituents, call for microscopic examination, 
in the course of which polarized light renders essential service, 
because these crystals, on account of their double refraction, 
appear much more distinct under the polarizing microscope 
than when observed in ordinary light. 
IX. Chemical constituents.—The enumeration and brief 
characterization of these principles essentially belongs to the 
functions of pharmacognosy. Under this heading are to be- 
considered not only the principles peculiar to certain drugs, 
but also the more commonly distributed constituents of plants. 
_ Though their isolation and quantitative estimation forms the 
object of chemical analysis,’ yet with the aid of micro-chemical 
reagents (see the concluding chapter of this book) it is possible 
to arrive in a short time at a series of valuable conclusions. 
regarding individual constituents. This method of procedure: 
especially affords information in many cases regarding the loca- 
_ tion of important constituents in the tissue. 
'G. Dragendorff : ‘‘ Die qualitative und quantitative Analyse von 
_ Pflanzen und Pflanzentheilen.” Gottingen, 1882 (see below, page 49). 
> 
