(_a_) _Squamous cells_: large, flat, polygonal cells with a comparatively small nucleus (Fig. 13, _i_). They come from the upper air-passages, and are especially numerous in laryngitis and pharyngitis. They are frequently studded with bacteria--most commonly diplococci. [Illustration: FIG. 13.--Different morphologic elements of the sputum (unstained): _a_, _b_, _c_, Pulmonary or alveolar epithelium--_a_, with normal lung pigment (carbon); _b_, with fat-droplets; _c_, with myelin globules; _d_, pus-corpuscles; _e_, red blood-corpuscles; _f_, cylindric beaker-shaped bronchial cells; _g_, free myelin globules; _h_, ciliated epithelium of different kinds from the nose, altered by coryza; _i_, squamous cells from the pharynx (after Bizzozero).] (_b_) _Cylindric cells_ from the nose, trachea, and bronchi (Fig. 13, _f_, _h_): These are not usually abundant, and, {43} as a rule, they are not identified because much altered from their original form, being often spheric. (_c_) _Alveolar cells_: rather large, round, or oval cells with one or two round nuclei (Fig. 13). Their source is presumably the pulmonary alveoli. Like the leukocytes, they frequently contain particles of carbon (normal lung pigment). In chronic heart disease, owing to long-continued passive congestion, they may be filled with brown granules of altered blood-pigment, and are then called "heart-failure cells" (Plate II, Fig. 1). Alveolar cells commonly contain fat-droplets and, less frequently, myelin globules. The latter are colorless, rounded bodies, sometimes resembling fat droplets, but often showing concentric or irregularly spiral markings (Fig. 13, _c_, _g_). They are also found free in the sputum. They are abundant in the scanty morning sputum of apparently healthy persons, but may be present in any mucoid sputum. (3) Red blood-corpuscles may be present in small numbers in almost any sputum. When fairly constantly present in considerable numbers, they are suggestive of phthisis. The corpuscles when fresh are shown by any of the staining methods which include eosin. They are commonly so much degenerated as to be unrecognizable, and often only altered blood-pigment is left. Ordinarily, blood in the sputum is sufficiently recognized with the naked eye. III. SPUTA IN DISEASE Only those conditions which give fairly characteristic sputa are mentioned. 1. Acute Bronchitis.--There is at first a small amount of tenacious, almost purely mucoid sputum, frequently blood-streaked. This gradually becomes more abundant, {44} mucopurulent in character, and yellowish or gray in color. At first the microscope shows a few leukocytes and alveolar and bronchial cells; later, the leukocytes become more numerous. Bacteria are not usually abundant.