PART III. 
REAGENTS. 
The reagents that have been recommended for 
microscopical work are quite numerous, and while 
nearly all of them may have more or less special 
merit, the number of reagents actually required in 
practice is fortunately quite small. 
It is important that the student recognize the neces- 
sity for a thorough understanding of the structure of 
the material under examination l'ather than place 
too much dependence upon the effects produced by 
reagents; in other words, the study of structure should 
precede the use of reagents, particularly stains, when 
it will often be found that the latter can be dispensed 
with entirely. 
The chemicals that are employed in microscopical 
work, either as reagents or for other purposes, may be 
classified as follows: (1) Preservatives, (2) Fixing and 
Killing Agents, (3) Hardening and Dehydrating 
Agents, (4) Clearing Agents, (5) Stains and (6) Special 
Reagents. 
Preservatives are substances used to preserve material 
which is to be examined. The most important of these 
are alcohol (from 40 to 95 per cent.) and formalin 
[2 to 6 per cent, in either aqueous or alcoholic (60 per 
cent, alcohol) solution], the latter of which is con- 
sidered advantageous in the preservation of specimens 
containing coloring substances, as leaves, flowers, etc. 
Almost any antiseptic of the proper strength may be 
used as a preservative. 
