108 Transactions of the Boyal Microscopical Society. 
of some of the more suitable staining reagents, and it is necessary 
to remark that it is at present in the condition most suitable for 
histo-chemical research ; the slightest tinting with a weak carmine 
solution just sufficient to render the cell elements visible enables the 
micros( opist to apply his reagents to great advantage ; at the same 
time metallic impregnation may be employed, as by the salts of gold, 
silver, platinum, or the hyperosmic acid. The dyes which I usually 
employ are the aniline and carmine solutions. The former as a 
1 per cent, solution of aniline black is pre-eminently useful for 
staining the cells of the cortex and their processes, whilst carmine 
deserves the preference for the best differentiation of the delicate 
neuroglia basis or framework of the nervous system. The staining 
with aniline is thus accomplished : a large drop of the solution is 
placed on the film, which in a short time begins to assume a 
general and decided coloration. When the requisite colour has been 
acquired (a matter learned by experience only) the slides are trans- 
ferred to a vessel containing water, and very gently lowered and 
allowed to rest on the flat bottom of the vessel. This immer- 
sion favours the staining and differentiation, for it will be observed 
that, as the superfluous dye floats away, aided by the gentle sway- 
ing to and fro of a brush in the fluid above, the film becomes deeper 
in hue and the staining perfectly uniform. The slide is now as 
carefully removed, all fluid drained ofl", and the preparation trans- 
ferred to a bell-glass which protects it from injury and dust during 
the process of drying which it has next to undergo prior to 
mounting. 
Third Stage. — Before the specimen can be permanently mounted 
in balsam it must necessarily undergo complete dehydration. For 
this purpose three methods present themselves for our choice, viz. 
1. Spirit. 2. Artificial heat. 3. Spontaneous drying beneath the 
bell-glass, with or without the agency of concentrated sulphuric 
acid. The first method I have now completely discarded, as present- 
ing numerous objections. The employment of artificial heat is also 
as far as possible to be avoided except where time is a matter of 
great import. The latter method is according to my own experience 
decidedly the best, and the addition of a small vessel of concentrated 
sulphuric acid beneath the bell-glass covering the slides very 
materially hastens the drying without in any way interfering with 
the delicate structures exposed in the slides. When perfectly dry 
a few drops of chloroform are placed over the film, which if 
examined in this moistened condition displays exquisitely the 
minute structure of the cortex. The chloroform must not be 
allowed to remain any length of time, a few seconds sufficing, and 
ere evaporation occurs a drop of a benzole or chloroform solution of 
Canada balsam is allowed to fall on the preparation, the cover-glass 
adjusted and gently pressed down. Oil of cloves may precede the 
