Eosinophilia may be a symptom of infection by any of the worms. It is fairly constant in trichinosis, uncinariasis, filariasis, and echinococcus disease. In this country an unexplained marked eosinophilia warrants examination of a portion of muscle for Trichina spiralis ([p. 255]).
True bronchial asthma commonly gives a marked eosinophilia during and following the paroxysms. This is helpful in excluding asthma of other origin. Eosinophiles also appear in the sputum in large numbers.
In myelogenous leukemia there is almost invariably an absolute increase of eosinophiles, although, owing to the great increase of other leukocytes, the percentage is usually diminished. Dwarf and giant forms are often numerous.
Scarlet fever is frequently accompanied by eosinophilia, which may help to distinguish it from measles.
Eosinophilia has been observed in a large number of skin diseases, notably pemphigus, prurigo, psoriasis, and urticaria. It probably depends less upon the variety of the disease than upon its extent.
(f) Basophilic Leukocytes or "Mast-cells" ([Plate VI]).—In general, these resemble polymorphonuclear neutrophiles except that the nucleus is less irregular and that the granules are larger and have a strong affinity for basic stains. They are easily recognized. With Wright's stain the granules are deep purple, while the nucleus is pale blue and is nearly or quite hidden by the granules, so that its form is difficult to make out. These granules are not colored by Ehrlich's stain.
The nature of mast-cells is undetermined. They probably originate in the bone-marrow. They are least numerous of the leukocytes in normal blood, rarely exceeding 0.5 per cent., or 25 to 50 per c.mm. A notable increase is limited almost exclusively to myelogenous leukemia, where they are sometimes very numerous.
(2) Abnormal Varieties.—(a) Myelocytes ([Plate VI]).—These are large mononuclear cells whose cytoplasm is filled with granules. Typically, the nucleus occupies about one-half of the cell, and is round or oval. It is sometimes indented, with its convex side in contact with the periphery of the cell. It stains rather feebly. The average diameter of this cell (about 15.75 µ) is greater than that of any other leukocyte, but there is much variation in size among individual cells. Myelocytes are named according to the character of their granules—neutrophilic, eosinophilic, and basophilic myelocytes. These granules are identical with the corresponding granules in the leukocytes just described. The occurrence of two kinds of granules in the same cell is rare.
Myelocytes are the bone-marrow cells from which the corresponding granular leukocytes are developed. Their presence in the blood in considerable numbers is diagnostic of myelogenous leukemia. The neutrophilic form is the less significant. A few of these may be present in very marked leukocytosis or any severe blood condition, as pernicious anemia. Eosinophilic myelocytes are found only in myelogenous leukemia, where they are often very numerous. The basophilic variety is less common, and is confined to long-standing severe myelogenous leukemia.
(b) Atypical Forms.—Leukocytes which do not fit in with the above classification are not infrequently met, especially in high-grade leukocytosis, pernicious anemia, and leukemia. The nature of most of them is not clear, and their number is usually so small that they may be disregarded in making a differential count. Among them are: (a) Border-line forms between polymorphonuclear neutrophiles and neutrophilic myelocytes; (b) small neutrophilic cells with a single round, deeply staining nucleus: they probably result from division of polymorphonuclear neutrophiles; (c) "irritation forms"—large non-granular mononuclear cells, whose cytoplasm stains fairly deep purple with Wright's stain, and intense brown with Ehrlich's: they appear in the blood under the same conditions as myelocytes; (d) degenerated forms: vacuolated leukocytes, or merely palely or deeply staining homogeneous or reticulated masses of chromatin ([Plate VI]).