Chapter XIX

THE PRESERVATION OF MACROSCOPIC PREPARATIONS.

For preserving gross objects for museum specimens alcohol or formol may be employed. The former bleaches the tissues so that ultimately they are almost destitute of color. Formol in a 5 per cent solution gives better color-effects than alcohol, as the blood-containing parts remain darker. The fluid also remains clear and the tissues are firm. When alcohol is used the fluid must be frequently changed, as it becomes turbid and yellowish, and the tissues finally become soft and lose their form. The best methods of preserving the natural color are found in the various modifications of the =Kaiserling method=. The organs or tissues are placed first in a formol solution until they are just hardened, the formol changing the oxyhæmoglobin into acid hæmatin. They are then transferred to alcohol to bring back the natural color, which is accomplished by the change of the acid hæmatin to an alkali hæmatin, which has a color very closely resembling that of oxyhæmoglobin, so that the natural color is approximately reproduced. The method is carried out as follows:—

Sol. I.—Formalin 200 cc.
Water 1,000 cc.
Potassium nitrate 15 grms.
Potassium acetate 30 grms.

The tissues are left in this solution, in the dark, for one to
several days, being watched carefully to see that they are not
over-hardened.

Sol. II.—80 per cent alcohol for 1-6 hours and then 95 per cent
until the color is fully restored (2-24 hours). Watch carefully and
remove as soon as best color effect is reached, and preserve in—

Sol. III.—Glycerin 400 cc.
Water 2,000 cc.
Potassium acetate 200 grms.

The specimens must be kept in air-tight jars, and crystals of
thymol added to prevent growth of moulds. This is sometimes very
difficult, and it becomes necessary to change the discolored fluid
for clear. I have found the rectangular museum jars best adapted
for the preservation of Kaiserling specimens. I use a wooden top
which fits over a thick piece of felt cut just the size of the
jar, which in turn fits over a piece of dental rubber cut to fit
the jar. The jar is placed upon a wooden bottom which has upright
steel rods at the corners, that pass through holes in the wooden
top, and have a screw-thread so that they can be fitted with
screws, which when screwed down hold the wooden top, felt and
rubber sheeting tightly in place, making the jar air-tight, but
giving a top easily removable. Very beautiful specimens can be
secured by the Kaiserling method, and they can be kept for several
years, but sooner or later the color-effect is lost. Light, heat
and exposure to the air cause a loss of color.

Some workers prefer the following in place of Sol. I:—

Hot water 2,000 cc.
Sodium sulphate 40 grms.
Magnesium sulphate 40 grms.
Sodium chloride 20 grms.

When salts are dissolved and solution cool add 200 cc. of formalin.

Melnikow-Raswedenkow Method:—

Sol. I.—Water 100 parts
Formol 10 parts
Sodium acetate 3 parts
Potassium chlorate 0.5 part

Leave in this 1-2-3-4-5 days, according to size of specimen. Large
organs must have solution injected into vessels.

Sol. II.—95 per cent alcohol, until color is restored.

Sol. III.—Preserve in: Water 100 parts
Glycerin 60 parts
Potassium acetate 30 parts

Pick’s Method:—

Sol. I.—Water 1,000 cc.
Formol 50 cc.
Carlsbad salts 50 grms.

Then transfer to 80 and 95 per cent alcohols, as for Kaiserling,
and preserve in water 9,000 cc., glycerin 5,400 cc., sodium acetate
2,700 grms.

=Westenhoeffer’s method= of preserving uric-acid: formol vapor 4-24
hours, then 80-90 per cent alcohol containing mercuric oxide, and
preserve in glycerin to which some mercuric oxide covered by cotton
or absorbent paper has been added.

=Claudius’s Method.= The specimen is placed on a grating in a
closed vessel containing a concentrated solution of ammonium
sulphate, an abundance of the crystals being left on the bottom of
the vessel. Carbonic acid or illuminating gas is passed through the
ammonium sulphate solution for 48-72 hours, and the specimens are
then preserved in the same solution. My experience with this method
has not been satisfactory.

=Gelatin method= of mounting Kaiserling preparations: Soak washed
Gold Label gelatin in distilled water for 12-24 hours. Take equal
parts of water-logged gelatin and glycerin and dissolve by heating
in a double boiler, stirring, for 15-20 minutes. Cool to 40°C.
Then clarify with white of egg (well-whipped whites of three eggs
to half a gallon of jelly: stir well; steam for ½ hour) and filter
through cotton-wool. Add to jelly a few drops of a weak aqueous
solution of crystal violet to remove yellow color (_Bruère and
Kaufmann_). To prevent growth of bacteria a small percentage of
formol or crystal of phenol may be added. Kaiserling specimens are
placed in glass dishes in the melted jelly, and covered with it.
When set the dishes containing the mounted specimens may be covered
with glass-plates and fastened to these by balsam or cement. I use
a deep Petri dish, filling it about two-thirds full with the jelly;
over this I pour melted paraffin of a very low melting point so as
not to melt the jelly. When the layer of soft paraffin is hard, a
thick layer of paraffin of a 52° melting-point is poured over it,
and the dish filled even. When the hard paraffin is set, it is
varnished with shellac. Liquefaction of the gelatin by bacteria or
enzymes constitutes the great drawback to this method.