162 THE AMERICAN MONTHLY [September, 
The sections are cut into water, to which it is advisable to add one-third 
glycerin, and allowed to remain a short time to remove the gum; they are 
then stained in any of the aqueous stains and mounted in glycerin; or they 
may be preserved in the following : — 
R. Glycerin, 
Aque dist., aa f 3 iv, 
Acid carbolic, gtt. iii 
M. Boil and filter. 
Beran Lewis treats brain sections cut by the freezing method with 0.25 
per cent. solution of osmic acid, to prevent the injurious effects of water-upon 
the sections. The sections are immersed for oze mznute in the osmic acid 
solution, which so ‘ fixes’ the elements that they are not dissociated by sub- 
sequent washing, staining, etc. The osmic acid must be thoroughly removed 
by washing in pure <Taliee , or the staining will be unsatisfactory. 
HARDENING AGENTS. 
Alcohol is an unsuitable hardening agent for brain and nervous centres. 
The tissue is contracted and distorted, and the alcohol dissolves and extracts 
much of the fatty constituents of nerve tissue, thereby injuring the minute 
structures considerably. The substances extracted are precipitated in the 
crystalline form, and as an amorphous, granular material. On microscop- 
ical examination the precipitate is and to consist largely of cholesterin and 
leucin. 
Spitzka has shown clearly that certain bodies found in the brains of the 
insane, and given such names as ‘ miliary sclerosis,’ ‘ colloid spheres,’ etc., 
are artificial “productions due to the precipitation of these alcoholic extrac- 
tives within the natural spaces of the tissue. 
Spitzka says :—‘ It is not certain but that the surprising amount of such 
precipitates found in hydrophobia, tetanus, death from strychnine poisoning, 
and acute delirium, as contrasted with other cerebral conditions, may indi- 
cate a previous chemical predisposition to dissociation of the nerve elements.’ 
If this be true, a certain value should be credited to alcohol as a chemical 
reagent, if not as a hardening agent. 
The use of the solutions of chromic acid and its salts is to be preferred in 
the hardening of nervous tissue for microscopical purposes. Of these the 
most useful is Miiller’s fluid.* It is a slow hardening agent; but this is the 
only objection to it. Large pieces will harden in it, there is no appreciable 
shrinkage, and the sections stain well. The growth of fungi may be pre- 
vented by keeping the jars in a refrigerator or by keeping a piece of camphor 
in the fluid. 
Four or five weeks are required to harden brain tissue. A whole or half 
brain will require longer; but hardening of large masses may be facilitated 
by making incisions into different parts, still keeping everything zz sztz. 
The membranes should zo¢ be removed. 
A more rapid hardening agent is made by substituting sulphate of copper 
for the sulphate of soda in Miiller’s fluid. It is known as Erlitzky’s (or 
Erlick’s) fluid, and is made as follows :— 
Potassium bichromate, 24 parts. 
Copper sulphate, 4 part. 
Water, 100 parts. 
This fluid will harden specimens in 8 or 10 days at the ordinary tempera- 
ture without injury to the nerve tissues. 
* Miiller’s Fluid. 
R. Potassium bichromate, 2 parts. 
Sodium sulphate, I we 
Distilled water, TOO) - 
ae 
