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.