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. {183} 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. 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.