APPARATUS AND METHODS.--The collections of most value, especially to our
various agricultural colleges and experiment stations will be largely of
a biologic and economic character, and the interest attaching to a
knowledge of the life history of insects will induce many collectors to
build up independent biologic collections. Very much of this biological
material will be alcoholic, and though many immature states of insects
may be preserved by dry processes, still the bulk must needs be kept in
liquid. This material may, when not abundant, be kept with the general
systematic collection, but experience has shown that it is better to
make a separate biological collection, and this is recommended
especially for State institutions where the collections may be expected
to attain some considerable proportions. In the case of such collections
it is very desirable to adopt some method of securing the vials in such
a manner that they can easily be transferred from one place to another
and fastened in the boxes or drawers employed for pinned insects. For
directions in this regard I reproduce from an article on the subject in
_Insect Life_, Vol. II, pp. 345, 346, which was republished, with slight
changes, from my annual report for 1886 as Honorary Curator.[7]
[7] Annual Report of the Smithsonian Institution for 1886, Part II,
Report of the National Museum, pp. 182-186. Washington, 1890.
_Vials, Stoppers and Holders._--The vials in use to preserve such
specimens as must be left in alcohol or other liquids are straight glass
tubes of varying diameters and lengths, with round bottom and smooth
even mouth. The stoppers in use are of rubber, which, when tightly put
into the vial, the air being nearly all expelled, keep the contents of
the vial intact and safe for years.
Various forms of bottles are used in museums for the preservation of
minute alcoholic material. I have tried the flattened and the square and
have studied various other forms of these vials; but I am satisfied that
those just described, which are in use by Dr. Hagen in the Cambridge
Museum, are, all things considered, the most convenient and economical.
A more difficult problem to solve was a convenient and satisfactory
method of holding these vials and of fastening them into drawers or
cases held at all angles, from perpendicular to horizontal. Most
alcoholic collections are simply kept standing, either in tubes with
broad bases or in tubes held in wooden or other receptacles; but for a
biologic collection of insects something that could be used in
connection with the pinned specimens and that could be easily removed,
as above set forth, was desirable. After trying many different
contrivances I finally prepared a block, with Mr. Hawley's assistance,
which answers every purpose of simplicity, neatness, security, and
convenience. It is, so far as I know, unique, and will be of advantage
for the same purpose to other museums. It has been in use now for the
past six years, and has been of great help and satisfaction in the
arrangement and preservation of the alcoholic specimens, surpassing all
other methods for ease of handling and classifying.
The blocks are oblong, one-fourth of an inch thick, the ends (_c c_,
Fig. 112) beveled, the sides either beveled or straight, the latter
preferable. They vary in length and breadth according to the different
sizes of the vials, and are painted white. Upon the upper side of these
blocks are fastened two curved clamps of music wire (_b b_), forming
about two-thirds of a complete circle. The fastening to the block is
simple and secure. A bit of the wire of proper length is first doubled
and then by a special contrivance the two ends are bent around a mandrel
so as to form an insertion point or loop. A brad awl is used to make a
slot in the block, into which this loop is forced (_e_, Fig. 112, 5), a
drop of warm water being first put into the slot to soften the wood,
which swells and closes so firmly around the wire that considerable
force is required to pull it out. Four pointed wire nails (_d d d d_),
set into the bottom so as to project about one-fourth inch, serve to
hold the block to the cork bottom of the case or drawer in which it is
to be placed. The method of use is simple and readily seen from the
accompanying figures, which represent the block from all sides.
The advantages of this system are the ease and security with which the
block can be placed in or removed from a box; the ease with which a vial
can be slipped into or removed from the wire clamps; the security with
which it is held, and the fact that practically no part of the contents
of the vial is obscured by the holder--the whole being visible from
above.
The beveled ends of the block may be used for labeling, or pieces of
clean cardboard cut so as to project somewhat on all sides may be used
for this purpose, and will be held secure by the pins between the block
and the cork of the drawers.
[Illustration: FIG. 112.--Vial holder; 1, block, with vial, beveled on
all sides; 2, do., beveled only on ends; 3, block, end view; 5, do.,
section; 4, 6, do., side views; _a_, block; _b_, spring-wire clamps;
_c_, beveled ends of block; _d_, pointed wire nails; _e_, point of
insertion of clamp. (Lettering on all figures corresponds.)]
The use of rubber stoppers in this country was first instituted by Dr.
H. A. Hagen in connection with the Cambridge biological collection, and
he has made some very careful records to determine the durability of
such stoppers. From an examination of some seven thousand vials with
rubber stoppers, two-thirds of which had been in use for from ten to
twelve years, he comes to the conclusion that less than one in a
thousand gives out every year after twelve years' use, and in the first
six years probably only one out of two thousand. Stoppers of large size
keep much longer than those of small size. American rubber stoppers are
all made of vulcanized India rubber and have the disadvantage of forming
small crystals of sulphur about the stopper, which become loosened and
attach themselves to the specimens. It is supposed that pure
rubber-stoppers used for chemical purposes would not present this
disadvantage, which may be obviated, however, or very much reduced, if
the stoppers are washed or soaked, preferably in hot water, for an hour
or two at least.
If stoppers are stored for a considerable time and exposed to the air
they become very hard and unfit for use, and Dr. Hagen has drawn
attention to a method recommended by Professor W. Hemple, of Dresden,
Saxony, of preventing them from becoming thus hardened. He says that to
keep rubber stoppers or rubber apparatus of any sort elastic, they
should be stored in large glass jars in which an open vessel containing
petroleum is placed. This treatment prevents the evaporation of the
fluids which are fixed in the rubber in the process of vulcanization. It
is better also to keep the light from the jar. To soften stoppers which
have already become hardened, they should be brought together in a jar
with sulphuret of carbon until they are pliable and afterward kept as
recommended above.
In the use of the rubber stopper the novice may find some difficulty in
inserting it in a vial filled with alcohol. The compression of the
alcohol, or alcohol and air when the vial is not completely filled,
forces the stopper out, and this is true whether of rubber or cork. If a
fine insect pin is placed beside the cork when this is thrust into the
bottle, the air or liquid displaced by the cork will escape along the
pin and the latter may then be removed and the cork remains securely in
position.
If cork stoppers have been used the vials may be stored in large
quantities together in jars filled with alcohol. This will prevent
evaporation of the alcohol from the vials, and the specimens may be
preserved indefinitely. This is only desirable in the storage of
duplicate specimens and unarranged material and is not recommended as a
substitute for the use of the rubber stopper. With cork stoppers
evaporation can be in a measure prevented if the cork is first anointed
with the petroleum preparation known as vaseline. This substance is
practically unaffected at ordinary temperature and is sparingly soluble
in cold alcohol. Experiments with it have shown that at ordinary spring
and summer temperatures there is no appreciable loss of alcohol from
vials and jars.
My old method of keeping alcoholic specimens, which I abandoned for the
method outlined above, was fairly serviceable, inexpensive, and warrants
description.
I had special folding boxes constructed resembling in exterior
appearance a large insect box. The bottom of the box was solid and was
made by gluing together two 11/2-inch planks.
Holes extending nearly through the lower plank and of various sizes to
accommodate vials of different diameters were bored as closely together
as the wood justified without splitting or breaking.
The holes were numbered consecutively and the vials when placed in them
were numbered to correspond; the box also had its number, and in the
notes the vial was referred to by number of box and vial thus, 3/73 (box
3, vial 73). The vial should project one-half to 1 inch above the hole,
and should be loose enough to provide for the swelling of the wood in
moist weather.
To protect the vials a cover having a depth of about 11/2 inch was hinged
to the back and secured in front by hook-and-eye fastenings.
This method of storing vials is satisfactory enough for private
collections, but for larger public collections is not so suitable.
[Illustration: FIG. 113.--The Marx tray for alcoholic specimens
(original.)]
A rather convenient and inexpensive method of storing vials is that used
by Dr. Marx. In this method the vials are stored in a wooden frame,
shown at Fig. 113. The top piece of the tray into which the vials are
thrust has a cork center, in which holes corresponding to the size of
the vials are made with a gun-wad punch. The outer end of the tray bears
a label or labels describing the material in the tray. The vials used by
Dr. Marx are of thinner glass than those which I recommend and flare
slightly at the top, as shown in the accompanying illustrations. They
are made in various sizes to accommodate larger and smaller specimens. A
vial thrust into the hole punched in the cork rests on the bottom piece
of the tray, the flange or neck preventing it from sliding through.
These trays are arranged on shallow shelves in a case or cabinet,
especially constructed for the purpose and a large quantity of material
may be stored by their use in small compass. The use of the cork center
piece in the upper part of the tray is not a necessity, and a wooden
piece may be used in which holes are bored with a bit of proper size.
[Illustration: FIG. 114.--Vials used in the Marx tray (original.)]
_Preserving Micro-larvae in Alcohol._--The following is quoted from
Packard's "Entomology for Beginners," for which it was translated from
the "_Deutsche Ent. Zeitg._," 1887, Heft I:
"Dr. H. Dewitz mounts the larvae and pupae of Microlepidoptera, and also
the early stages of other small insects, in the following way: The
insects are put into a bottle with 95 per cent alcohol. Many larvae turn
black in alcohol, but boiling them in alcohol in a test tube will bleach
them. They may then be finally placed in glass tubes as small and thin
as possible, varying from 0.003 to 0.006 meter in diameter, according
to the size of the insects. About 0.07 meter's length of a tube is
melted over a spirit lamp, and the tube filled three-quarters full with
95 per cent alcohol, the insects placed within and the contents of the
tube heated at the end still open, and then closed by being pulled out
with another piece of glass tubing. After the glass has been held a few
minutes in the hand until it is slightly cooled off, the end closed last
is once more held over the lamp so that the points may be melted
together, and this end of the glass may be finished. During the whole
time from the closure of the tube until the complete cooling of the
glass it should be held obliquely in the hand, so that the alcohol may
not wet the upper end, for if the tube is too full it is difficult to
melt it, as the steam quickly expanding breaks through the softened mass
of glass. The tube may be mounted by boring a hole through a cork
stopper of the same diameter as the glass. The stopper is cut into the
shape of a cube, a strong insect pin put through it, and the glass tube
inserted into the hole. It can then be pinned in the insect box or
drawer, near the imago, so that the free end of the glass may touch the
bottom, while the other end stands up somewhat; while to keep the tube
in place the free end resting on the bottom may be fastened with two
strong insect pins. The specimens thus put up can easily be examined
with a lens, and if they need to be taken out for closer examination the
tube can be opened and closed again after a little practice."
[Illustration: FIG. 115.--Method of preserving minute larvae etc. (After
Dewitz.)]
PRESERVATIVE FLUIDS.--The principal liquids in which soft-bodied insects
may be successfully preserved are the following:
_Alcohol._--As indicated in the foregoing portions of this work, alcohol
is the standard preservative used for soft-bodied specimens, and may be
used either full strength or diluted with water. Diluted alcohol should
always be first used with larvae, since the pure alcohol shrivels them
up. The weak spirits can afterwards be replaced by strong, for permanent
preservation.
_Alcohol and White Arsenic._--The method of preserving insects
recommended by Laboulbene and quoted in Packard's Entomology for
Beginners, consists in plunging the insects in the fresh state into a
preservative liquid, consisting of alcohol with an excess of the common
white arsenic of commerce. The larva placed in this mixture absorbs .003
of its own weight, and when removed and pinned is safe from the attacks
of museum pests. This liquid is said not to change the colors, blue,
green or red of beetles, if they are not immersed for more than
twenty-four hours. This treatment is applicable to the orders
Coleoptera, Hemiptera, and Orthoptera. If the insect is allowed to stay
in this mixture for a considerable time, say three or four weeks, and
then removed and dried, it becomes very hard and brittle and can not be
used for dissection or study, but makes a good cabinet specimen. The
white deposit of arsenic which will appear on drying can be washed off
with alcohol.
_Alcohol and Corrosive Sublimate._--The same author recommends another
preparation consisting of alcohol with a variable quantity of corrosive
sublimate added, the strength of the solution varying from 100 parts of
alcohol to 1 part of corrosive sublimate for the strongest, to one-tenth
of 1 part of sublimate in 100 parts of alcohol for the weakest. The
insects are allowed to remain in this mixture not longer than two hours
before drying. The last-described preparation is said to preserve the
specimens from mold. Both of these solutions are very poisonous and
should be used with care.
_Two Liquids to preserve Form and Color._--Professor Packard also quotes
the formula of A. E. Verrill for preserving insects in their natural
color and form. Two formulas are given; the first consists of 21/2 pounds
of common salt and 4 ounces of niter dissolved in a gallon of water and
filtered. The specimens should be prepared for permanent preservation in
this solution by being previously immersed in a solution consisting of a
quart of the first solution and 2 ounces of arsenite of potash in a
gallon of water. Professor Packard gives also the formula of M. H. Trois
for preserving caterpillars, for which it is claimed that the colors of
the caterpillars are preserved perfectly, even when exposed to strong
light. The formula for this solution is as follows:
Common salt grams 2.35
Alum do. 55
Corrosive sublimate centigrams 18
Boiling water liters 5
Allow the liquid to cool and add 50 grains of carbolic acid, and filter
after standing five or six days.
_Glycerin._--Glycerin, either pure or mixed with water or alcohol, is
frequently used to preserve the larvae of delicate insects. It preserves
the color and form better than alcohol, but particularly in the case of
larvae, it causes a softening of the tissues which renders them unfit for
study.
_The Wickersheim Preserving Fluid._--This valuable preserving fluid has
been known for some time, but is not very commonly used, on account of
frequent disappointment due to the difficulty attending its preparation.
It is claimed for it that animal or vegetable bodies impregnated with it
will retain their form, color, and flexibility in the most perfect
manner. The objects to be preserved are put in the fluid for from six to
twelve days, according to their size, and then taken out and dried in
the air. The ligaments remain soft and movable, and the animals or
plants remain fit for anatomical dissection and study for long periods,
even years. It is said to be especially valuable for the preservation of
larvae and soft-bodied insects. In order to perfectly preserve the
colors, it is necessary to leave the specimens in the fluid, or, if they
are taken out, they should be sealed up in air-tight vials or vessels.
The formula for the fluid is as follows:
Dissolve 100 grams alum, 25 grams common salt, 12 grams saltpeter, 60
grams potash, 10 grams arsenious acid in 3,000 grams boiling water.
Filter the solution, and when cold add 10 liters of the liquid to 4
liters of glycerin and 1 liter of methyl alcohol.