Comparative Hæmocytology of Laboratory Animals

Totals Percentages

Animal Red cells White cells Hb, per cent. Lymphocytes, per cent. Large monos, per cent. Polymorph, per cent. Eosinoph, per cent. Mast cells, per cent.

Frog 490,000 8,000 58 40 10.0 22.0 15 13

Mouse 8,700,000 8,000 78 60 21.5 17.0 1.4 0.1

Rat 9,000,000 9,000 85 54 7.0 37.5 1.3 0.2

Guinea-pig 5,700,000 10,000 99 55 9.0 32.8 3.0 0.2

Rabbit 6,000,000 7,000 70 50 2.0 46.0 0.6 1.4

Rhesus 4,500,000 13,000 77 43 5.0 50.0 1.3 0.7

Goat 14,600,000 15,000 58 35 6.3 56.7 1.25 0.75

Fowl 3,500,000 30,000 100 49 3.0 42.0 1.0 5.0

Pigeon 3,500,000 20,000 101 43 9.0 43.0 3.0 2.0

Man(adult) Normal limits. 5,000,000 (4.5-5) millions. 7,500 (7-9) thousands. 100 (95-101) 25 (20-30) 5.5 (4-8) 65 (55-68) 4.0 (3-5) 0.5 (0.5-2)

The above table represents in each case the average of a large number of counts.

Remarks.

Frog.—The red cells are large oval nucleated (20-25µ by 12-15µ) discs, the nucleus relatively small and irregularly elongated or oval, about 10µ in length. Many primitive and developing forms are usually observed—also free nuclei and many cells in various stages of degeneration. Hæmoglobin estimation is difficult owing to turbidity of the blood after dilution with water. The polymorphonuclear leucocytes are large cells, about 20µ; no definite granules can be observed. The eosinophile cells contain large deeply staining coccal-shaped granules.

Mouse.—The granules of the polymorphonuclear leucocytes are usually not stained, or only very faintly so. The nucleus of the eosinophile cell is ring-shaped or much divided, and the granules are coccal and stain oxyphile. The remarkable character of the blood is the high percentage of large mononuclear cells.

Rat.—The fine rod-shaped granules of the polymorphonuclear leucocytes are usually very faintly stained. The granules of eosinophile cells are well stained and coccal-shaped, the nucleus is often ring shaped. The basophile granular cells are few—but the granules are large, and stain deeply basophile.

Guinea-pig.—Polychromasia and punctate basophilia of red cells are very commonly observed—nucleated red cells are also frequent. The large mononuclear cells often contain vacuoles—"Kurlow cells"—possibly of a parasitic nature.

Rabbit.—It is not uncommon to find nucleated red cells in films from quite healthy animals. The granules of the polymorphonuclear leucocytes stain oxyphile. The coarse granules of the eosinophile cells appear to stain less deeply oxyphile, probably owing to the basophile staining of the cytoplasm.

Rhesus monkey.—The blood cells resemble those met with in human blood. The minute neutrophile granules of the polymorphonuclear leucocytes are often very scanty, and sometimes apparently absent. The eosinophile cells are not so densely packed with coarse oxpyhile granules as in the human eosinophile, and the nuclei of these cells are usually much divided, or polymorphous.

Goat.—The red cells are small, nonnucleated discs, only about 4.5µ diameter, not much more than half that of the human red cell. The polymorphonuclear leucocytes have only a few very minute coccal-shaped oxyphile granules, the nucleus is polymorphous. The eosinophile cells are large cells up to 20µ, the cytoplasm is basophile and contains coarse coccal-shaped oxyphile granules, and the nucleus is often much divided.

Fowl.—The red cells are oval nucleated discs about 12µ by 6µ, the nucleus being relatively small (about 4µ long), irregularly elongated or oval; round, more deeply stained cells with round or diffuse nuclei, also free nuclei and degenerated forms of red cells are often present. The granules of the cells corresponding to the polymorphonuclear leucocytes are rod-shaped, often beaded or with clubbed ends. The nucleus is not polymorphous, but usually divided into two, though it may be single. The cells probably corresponding to eosinophile leucocytes have fine coccal-shaped granules, faintly staining eosinophile or neutrophile. The basophile granules of the "mast" cells are coccal-shaped, of various size—often quite powdery.

Pigeon.—Red cells resemble those of the fowl, and similar varieties of appearance may be noted. The granules of those cells which correspond to polymorphonuclear leucocytes are rod-shaped, but smaller and finer than in the fowl, and do not show clubbed appearances. The nucleus is not polymorphous, and only occasionally divided. The coccal-shaped granules of the eosinophile cells are stained more deeply oxyphile than those of the corresponding cells of the fowl.

The preparation of dried films for this histological examination of the blood is carried out as follows:

1. Small samples of blood for the preparation of blood films are most conveniently obtained from the veins of the ear in most of the ordinary laboratory animals, viz., monkey, goat, dog, cat, rabbit, guinea-pig; in the pigeon and fowl the axillary vein should be punctured; in the rat and mouse either a vein in the ear or preferably by wounding the tip of the tail; in the frog, the web of the foot should be selected.

2. Puncture the selected vein with a sharp needle. A flat Hagedorn needle (size No. 8) with a cutting edge is the most useful for this purpose. If the vein cannot be distended by proximal compression, vigourous friction with a piece of dry lint may have the desired effect—or a test-tube full of water at about 40°C. may be placed close to the vein. Failing these methods, a drop or two of xylol may be dropped on the skin just over the vein, left on for a few seconds and then wiped off with a piece of dry lint.

3. One of the short ends of a 3 by 1 glass slip is brought into contact with the exuding drop of blood, so that it picks up a small drop.

4. The slide is then lowered transversely on to the surface of a second 3 by 1 slip, which rests on the bench near to one end at an angle of about 45°, and retained in this position for a few seconds, while the drop of blood spreads along the whole of the line of contact (see also Fig. 69).

5. Draw the first slide firmly and evenly along the entire length of the lower slide, leaving a thin regular film which will probably show the blood cells only one layer thick.

6. Allow the film to dry in the air.

7. Stain with one of the polychrome blood stains (see page 97).

8. Examine microscopically.

b. The bacteriological examination of the blood is directed solely to the demonstration of the presence in the circulating blood of the organisms previously injected into the animal. For this purpose several cubic centimetres of blood should be taken in an all-glass syringe from an accessible vein corresponding to one of those suggested as the site of intravenous inoculation—and under similar aseptic precautions.

1. Sterilise an all-glass syringe of suitable size, and when cool draw into the syringe some sterile sodium citrate solution and moisten the whole of the interior of the barrel; then eject all the citrate solution if less than 5 c.c. blood are to be withdrawn; if more than 5 c.c. are required retain about half a cubic centimetre of the fluid in the syringe. This prevents coagulation of the blood.

The sodium citrate solution is prepared by dissolving:

Sodium citrate 10 gramme.

Sodium chloride 0.75 grammes.

In distilled water 100 c.c.