Tue Microscope. 173 
duced. This method works especially well for demonstrating 
the nerves of the cornea, the cornea corpuscles, and the termi- 
nation of nerves in striated muscles. Gold is principally useful 
for staining nerve-fibrils and connective tissue corpuscles. 
OSMIC ACID. 
A one per cent. solution of this is made, and then reduced 
to a one-fourth or one-half per cent. solution, as required. It 
has already been referred to as a reagent that blackens fat cells 
and colors the white substance of Schwann in nerve fibres. 
MOUNTING. 
It is customary to mount the sections on glass slides three 
inches long and one inch wide. An effort has been made to 
change these dimensions; but as this would cause great incon- 
venience, the usual size should be adhered to, when possible. 
The slides should be ground on the ends and sides, and should 
be thin and clear. 
The cover glasses are either square or round. As a general 
rule the round covers are to be preferred. They are much bet- 
ter when the mount is to be placed in a cell, as cells are made 
round more quickly and evenly by the aid of the turn-table 
than they can be made square by the unaided hand; and they 
allow the slide to be neatly finished by running around the 
cover a little cement. Thin covers should be preferred; at least 
the thick covers sometimes found in No. 3 ought to be avoided 
except In special cases. 
The glass slides and covers, especially the latter, are gen- 
erally covered with a dirty oily film that is difficult to remove. 
They should be placed for a couple of hours in strong sulphuric 
acid; then removed, and water allowed to flow over them; then 
placed in alcohol, from which they are removed, one by one, 
and carefully rubbed clean with a silk handkerchief, or prefer- 
ably a piece of old soft linen or clean chamois. <A strong solu- 
tion of caustic soda will usually soften any of the hard sub- 
stances used in mounting. Old slides that have been used for 
mounting may be cleaned by placing them in this soda solution 
for a few hours. ; 
Slides and covers should always be thoroughly cleaned as 
described above, before using. 
