POWDERED DRUGS. 
265 
der it is necessary to employ reagents which render 
the particles more or less transparent and at the same 
time do not destroy their characteristics ; the most 
satisfactory reagent of this kind for general purposes 
is an aqueous solution of chloral or a solution of 
chloral and glycerin ; about a milligramme of the 
powder is mounted in a few drops of this solution, the 
preparation is gently heated, then allowed to cool, and 
examined ; if it is not sufficiently transparent, it is 
heated again. The reagent causes a swelling of the 
cell-wall and is not applicable in the study of the 
starch grains, but it is very useful in the study of 
mechanical tissues, hairs and calcium oxalate. 
After having determined the presence of starch, a 
separate mount of the powder in water is made and 
the size and markings of the grains noted. 
For the examination of more or less lignified cells, 
mounts are made, either in phloroglucin or aniline 
sulphate solution ; in some cases it is advantageous to 
apply these solutions after the specimen has been pre- 
viously treated with chloral. Sometimes it is desir- 
able to study the mechanical cells more closely, and 
Schulze’s macerating fluid or sulphuric acid may be 
used for isolating them. 
Examination. — All powders contain a greater or less 
amount of fragments of walls and other materials 
which are more or less alike in the different powders, 
and it is important that this fact be borne in mind in 
order that attention may be especially directed to those 
elements of the powder which have a diagnostic value. 
The latter are relatively few in number, easily identified 
and the distinguishing features readily determined in 
nearly all cases. And it is for this reason that separate 
illustrations are not considered necessary for the indi- 
vidual powders. The plates in Part IV of this book 
