_Preparation and Preservation of Material._--Formalin forms by far the
most satisfactory preservative for anatomical material. It is much
better in almost every respect than alcohol, and has the additional
advantage of being much cheaper.
After injecting with formalin, the cat may be preserved either immersed
in a weaker solution of the same substance, or may be kept for a long
time simply wrapped in a cloth dampened with formalin. The details of
preparation differ according to which method is to be used.
In either case, the cat should be killed with chloroform, by placing it
in a tight jar or box with a cloth or bit of cotton saturated with
chloroform. It is not necessary to bleed the specimen. When the cat is
dead, remove it to a tray, place it on its back, and tie the limbs
loosely so that they will remain outspread.
Expose the femoral artery in the thigh, as follows: Make a median
longitudinal incision through the skin of the abdomen, from a point an
inch or two caudad of the xiphoid process to the pubis. Make an incision
passing from near the middle of this obliquely laterad onto the thigh,
for about three inches. Reflect the two flaps in the angles between
these cuts, then with forceps and tracer isolate the femoral artery just
as it passes into the thigh (Fig. 127, _a_). Make with scissors an
oblique incision in one side of the artery, one-half to one inch from
the point where it leaves the abdominal cavity. Introduce a canula
directed toward the body, and tie it in place.
1. If the cat is to be preserved immersed in a solution of formalin, it
should now be injected with a five per cent. solution of commercial
formalin in ordinary water (commercial formalin 5 parts; water 95
parts). Into an adult cat 300 to 400 cubic centimeters of the five per
cent. formalin should be injected.
The cat may now be preserved in a one per cent. solution of formalin.
Before immersing it in the formalin it is well to remove the hair in
some way, otherwise this will hold much water and be very inconvenient
in dissection. The neatest method is to cut off the hair with scissors;
this takes some time, however. If the skin-muscles (p. 93) are not to be
dissected, the skin may be removed. It is well in this case to leave the
skin on the sides of the head and on the feet.
It is not necessary to open the abdominal cavity, after injecting with
the five per cent. formalin. If there is at any time reason to suspect
that the viscera are not keeping well, the abdominal and thoracic
cavities should be filled with five per cent. formalin by making a small
hole through the body wall into the cavity, introducing a canula, and
injecting till the cavity is full.
The specimen should be kept in a jar or other vessel and should be
completely immersed beneath the one per cent. formalin. Any parts
projecting above the fluid may be attacked by mould. If a part is found
to be moulded, it should be submerged, when the mould will be killed.
The mould injures the specimen if allowed to grow for a long time, but
if discovered soon, no very serious harm results.
During dissection, exposed parts of the body should be kept from drying
by covering with a damp cloth. Specimens preserved in formalin dry out
much less quickly than those preserved in alcohol.
2. For some purposes it is much more convenient to preserve the material
without immersing it in a vessel of formalin. Specimens injected with
five per cent. formalin, as above directed, would usually keep perfectly
without further treatment, but for two difficulties: (1) the specimen
may _dry_; (2) it may be attacked by mould.
The drying may be prevented as follows: Use for injecting a mixture of
the five per cent. formalin with one-sixth its volume of glycerine. This
will dry only very slowly, and if pains are taken to keep exposed parts
covered with cloths dampened with the mixture of formalin and glycerine,
there will be no trouble from this source. The skin should not be
removed from such specimens except as necessary in the course of
dissection. The hair will give little trouble, because dry.
The specimens should be kept in a tight box, that the fluid may not
evaporate rapidly from the cloths used for wrapping.
The attacks of the mould present a difficulty not so easily overcome. As
long as the specimens are in daily use for dissection, and exposed parts
kept covered with cloths saturated with the glycerine and formalin
mixture, little or no trouble is to be anticipated. But if the specimens
are left untouched for some days, and particularly if exposed surfaces
are not kept covered in the manner above recommended, mould is almost
sure to attack them. Material neglected for a week may thus be ruined.
If mould is found at any time to be attacking the material, the attacked
part should be cleaned and well wrapped in cloths saturated in the
formalin-glycerine mixture. If such means are unavailing, the specimen
should be immersed in a vessel of one per cent. formalin and preserved
for the future in this. Recourse should be had at once also to this
method of preservation if the specimen shows signs of decomposition by
having a strong odor.
It seems probable that the attacks of the mould might be prevented by
mixing some fungicide with the injecting fluid; experiments should be
made in this direction.
There are many advantages in preserving the material if possible without
immersing it. All parts retain their color and pliability much more
completely, so that the different structures are much more easily
distinguishable. The method above described, by the use of formalin and
glycerine, is to be recommended when the material is to be worked on
every day or so and is not to be kept longer than a few weeks. It is
usually not very satisfactory in warm weather, however. If some method
can be devised of entirely preventing the attacks of the mould, this
will be an excellent method of preserving anatomical material.
The same specimens used for the study of the muscles will serve also for
the spinal cord and brain if prepared by one of the methods above
described. (For the viscera, blood-vessels, and nerves, other specimens
will have to be prepared; for these, directions are given later.)
_Muscles to be Dissected._--It will probably usually be impossible in a
given course of study to dissect all the muscles of the cat. The
instructor will of course select such as seem most advisable to him. The
following may perhaps be recommended as a good selection for a fairly
extensive course: Muscles of the Fore Limbs (pp. 436-439); Muscles of
the Neck and the Deep Muscles of the Head (pp. 439-441); Muscles of the
Wall of the Thorax and of the Abdomen (pp. 441-442); Muscles on the
Ventral Side of the Neck (p. 442). If the superficial facial muscles
(excluding those of the ear) can be studied from a preparation, this
will be a valuable addition to a course (pp. 434-435).