Part 90

Soft water 2000 cc. Strong ammonia 150 cc. Nitrate of potash (saltpetre) 12 grams. Hard soap 75 grams.

Heat these together till a homogeneous mixture is formed. Now immerse the bone or bones to be cleaned in a liquid composed of four parts water to one part of the above liquid-soap mixture. Boil forty minutes; pour off the liquid and renew it. Boil about half an hour longer; then remove soft parts with fingers, scalpel, and brush. The bones may be boiled as much longer in the mixture as is necessary to make the soft parts come away easily. If they are boiled too long, however, the epiphyses will separate from the bones. This is especially likely to occur in young skeletons, which must therefore not be boiled so long as the bones of an old cat.

Skeletons prepared in the following rough way are useful for many purposes. The entire body of the cat, or a single limb, is placed in the liquid-soap mixture (after partial removal of soft parts), and boiled till the muscles may be removed, but the ligaments, holding the bones together, remain. Clean thoroughly without removing the ligaments, and allow to dry. The bones are thus held together in their natural positions. Skeletons so prepared are not elegant, but are frequently useful.

Disarticulation of Skulls.--The bones of the skull may be separated as follows: Clean the skull in the liquid-soap mixture, as above described. Then fill the cranial cavity with dry rice, beans, corn, or some other seeds that swell much on imbibition of water. Cork up the foramen magnum, and place the skull for twelve to twenty-four hours in water. The swelling of the grain will partially separate the bones at the sutures. The bones may then usually be separated completely by hand.

Entire skulls, and longitudinal sections, as represented in Fig. 43, p. 60, should be at hand.

Study of the Bones.--The bones should be studied in the order in which they are described. No further special directions for their study are necessary.

Study of Ligaments.--It will usually not be practicable for each student to make the dissections and preparations necessary for studying the ligaments. Rather should these be examined on demonstration preparations preserved in the laboratory. Such preparations may most easily be made by using fresh material, and dissecting away muscles and other tissues, leaving only the ligaments connecting the bones. The preparations are then preserved in one or two per cent. formalin. It is difficult to prepare the ligaments satisfactorily on preserved material, because they do not stand out clearly from other tissues in such material, so that they are not easily distinguishable.

MUSCLES.

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).

DISSECTION OF MUSCLES.

General.--In dissecting muscles a prime requisite of successful dissection is to keep the muscles clean. Fat, connective tissue, etc., is to be carefully but thoroughly cleared away from the surface of muscles and from between them. Frequently when it seems impossible to distinguish the structures described, all difficulty will vanish as soon as the dissection is thoroughly cleaned.