They are probably formed from the large mononuclears, and occur in the blood in about the same numbers. The two cells are usually counted together.
(d) Polymorphonuclear Neutrophilic Leukocytes ([Plate VI]).—There is usually no difficulty in recognizing these cells. Their average size is somewhat less than that of the large mononuclears. The nucleus stains rather deeply, and is extremely irregular, often assuming shapes comparable to letters of the alphabet, E, Z, S, etc. ([Fig. 86]). Frequently there appear to be several separate nuclei, hence the widely used name, "polynuclear leukocyte." Upon careful inspection, however, delicate nuclear bands connecting the parts can usually be seen. The cytoplasm is relatively abundant, and contains great numbers of very fine neutrophilic granules. With Wright's stain the nucleus is bluish-purple, and the granules, reddish-lilac.
Polymorphonuclear leukocytes are formed in the bone-marrow from neutrophilic myelocytes. They constitute 60 to 75 per cent. of all the leukocytes: 3000 to 7500 per c.mm. of blood. Increase in their number practically always produces an increase in the total leukocyte count, and has already been discussed under "phagocytic leukocytosis." The leukocytes of pus, pus-corpuscles, belong almost wholly to this variety.
A comparison of the percentage of polymorphonuclear cells with the total leukocyte count yields more information than a consideration of either alone. With moderate infection and good resisting powers the leukocyte count and the percentage of polymorphonuclears are increased proportionately. When the polymorphonuclear percentage is increased to a notably greater extent than is the total number of leukocytes, no matter how low the count, either very poor resistance or a very severe infection may be inferred. In the absence of acute infectious disease a polymorphonuclear percentage of 85 or over points very strongly to gangrene or pus-formation. On the other hand, except in children, where the percentage is normally low, pus is uncommon with less than 80 per cent. of polymorphonuclears.
Normally, the cytoplasm of leukocytes stains pale yellow with iodin. Under certain pathologic conditions the cytoplasm of many of the polymorphonuclears stains diffusely brown, or contains granules which stain reddish-brown with iodin. This is called iodophilia. Extracellular iodin-staining granules, which are present normally, are more numerous in iodophilia.
This iodin reaction occurs in all purulent conditions except abscesses which are thoroughly walled off or purely tuberculous abscesses. It is of some value in diagnosis between serous effusions and purulent exudates, between catarrhal and suppurative processes in the appendix and Fallopian tube, etc. Its importance, however, as a diagnostic sign of suppuration has been much exaggerated, since it may occur in any general toxemia, such as pneumonia, influenza, malignant disease, and puerperal sepsis.
To demonstrate iodophilia, place the air-dried films in a stoppered bottle containing a few crystals of iodin until they become yellow. Mount in syrup of levulose and examine with a one-twelfth objective.
(e) Eosinophilic Leukocytes, or "Eosinophiles" ([Plate VI]).—The structure of these cells is similar to that of the polymorphonuclear neutrophiles, with the striking difference that, instead of fine neutrophilic granules, their cytoplasm contains coarse granules having a strong affinity for acid stains. They are easily recognized by the size and color of the granules, which stain bright red with Wright's stain.
Eosinophiles are formed in the bone-marrow from eosinophilic myelocytes. Their normal number varies from 50 to 400 per c.mm. of blood, or 1 to 4 per cent. of the leukocytes. An increase is called eosinophilia, and is better determined by the actual number than by the percentage.
Slight eosinophilia is physiologic during menstruation. Marked eosinophilia is always pathologic. It occurs in a variety of conditions, the most important of which are: infection by animal parasites; bronchial asthma; myelogenous leukemia; scarlet fever; and many skin diseases.