Art. XI.—Formaline in Museology.
[Read before the Wellington Philosophical Society, 20th September, 1898.]
The liquid called “formaline,” or “formol,” represents a 40-per-cent. solution of formaldehyde in distilled water, and is likely to replace spirits of wine in many cases, and to improve the conditions and general aspect of preserved specimens. On its introduction into museology formaline was used indiscriminately, and in the same way as spirits, the result, of course, being, to a certain extent, the discrediting of the liquid. By degrees the limits of its use, the proper concentration, and its drawbacks have been observed, and in the following lines I give a short notice of my six years' experience.
Mammals, birds, and reptiles ought to be preserved in spirits in the usual way. Formaline does not penetrate the skin sufficiently, and, even after opening the abdomen, it is not possible to get a satisfactory result. Especially if the specimen is intended for anatomical dissection formaline must be avoided, because it entirely prevents the maceration of the skeleton. The only exception to this rule is that of a rare small mammal or bird, which, being badly shot, or spoiled, has to be preserved, skinning not being possible. In this case, after opening the abdomen and removing the intestines—except ovaries and testicles—a ball of cotton soaked in con-
centrated formaline is to be placed in the cavity, a similar one filling the throat. In a few days the specimen will be mummified, and may be kept. In larger specimens—e.g., pheasants—where the aorta is easily to be found, it is advisable to inject a quantity of concentrated formaline into the arteries before filling the abdomen with soaked cotton. This is to make sure of the preservation of the legs, arms, and head.
Large fish should be skinned or preserved in spirits after opening the abdomen, formaline being useful only for the smaller fish. The advantage of formaline lies in the preservation of the shape of the body and of the superficial slime covering the scales. Part of the colours, however, will fade away after a short time, as in spirits; the yellow, blue, pink, and violet adipochromes being soluble in formaline as well as in spirits.
The method for smaller fish is used, too, for Batrachia. The skin (epithelium) of both resists the penetration of formaline as strongly as that of a mammal or bird. The simple immersion of a fish in formaline will, of course, preserve the outside well, but the interior will, after some time, fall to pieces. To avoid this the specimens have to be injected. The solution used is 10 per cent. in fresh water; sea-water must be used for sea-fish. In each case the addition of 1 per cent. of kitchen salt will secure the specimen from looking swollen by the action of the formaline on the connective tissue. The said solution should be injected from the anus into the gut, from where it will slowly diffuse into the tissues of the body. In larger fish (8 in. and more), especially if they are of any depth—the distance from the abdominal cavity to the back fin exceeding 1 in.—after injecting the intestines a pointed cannula (hypodermic) is to be used in injecting the 10-per-cent. solution through the skin of the back into the muscles in several places. The same effect will be obtained by injecting the solution from the art. Cœliaca. After the injection the specimens of Batrachia and fishes are to be kept in a 1—2-per-cent. solution of formaline, with about ½—1 per cent. of kitchen salt. Small fish (1—2 in.) may be preserved without injection.
In evertebrates it is to be borne in mind that formaline is apt to destroy the small calcareous corpuscula contained in the skin of various animals—e.g., Synaptœ. Those, of course, are to be killed in the usual way—sea-water, with ether sulf.—and preserved in spirits. Spirits should be used for Crustacea and echinoderms, if they are not dried all together.
In insects it is often desirable to preserve gallæ, webs, cocoons, &c., containing eggs or small larvæ, together with
the branches, leaves, &c., upon which they are found. The easiest way is to put the whole branch or leaf into a glass tube or jar, and a few drops of concentrated formaline on the bottom of the glass, which will soon evaporate and preserve the object. The glass has to be kept air-tight and well closed. Cephalopoda are kept in a 2-per-cent. solution of formaline in sea-water, which has to be changed several times. It is advisable to inject a small quantity of the same solution into the siphon of the animal.
Shellfish, oysters, &c., are kept in the same way after opening the shells, or removing one of them entirely. To avoid the changing of the solution, the animal may as well be killed by pouring boiling water over it. After a few minutes the coagulation of the albumen will be finished, and the specimen may be mounted at once in the 2-per-cent. solution in sea-water. In the same way slugs and snails may be treated. To avoid the contraction of the body, before pouring out the boiling water they should be anæsthetized or killed in sea-water mixed with ether sulf. or cocaine. Generally the Tunicata may be preserved in the same way, if possible using living animals. This is indispensable with Medusœ, Salpœ, Pyrosomœ, &c. The best plan is to put them immediately from the net into a 10-per-cent. solution of formaline in sea-water. They die in a few seconds, and coming home you can select the specimens you require, which should be mounted in a fresh 10-per-cent. solution. Siphonophorœ have to be killed in another way, to avoid the dismembering. The animal is kept in as little sea-water as possible, in a much larger (higher) jar. Then a large quantity of a solution of cupr. sulf. (25 per cent.) is at once poured over it. After an hour or less the specimen may be placed in a 2-per-cent. solution of formaline in sea-water. Sea-worms, Aphroditœ, &c., do not keep in formaline. They are killed in a concentrated solution of corrosive sublimate, and after about ten minutes washed out in a weak solution of spirits of wine, and mounted in a spirit of about 80–90 per cent.
Specimens of any description which have been hardened and preserved in spirits of wine may, without inconvenience, be placed and kept in a 2-per-cent. solution of formaline, the mixture of spirits and formaline being of no consequence. Vertebrates, however, after a certain time will not be fit for dissection and maceration, while Synaptcœ, etc., will have their calcareous formations destroyed.