The portions most likely to contain structures of interest should be very carefully selected, as already described. _The few minutes spent in this preliminary examination will sometimes save hours of work later._ Opaque, white or yellow particles are frequently bits of food, but may be cheesy masses from the tonsils; small cheesy nodules, derived from tuberculous cavities and containing many tubercle bacilli and elastic fibers; Curschmann's spirals, or small fibrinous casts, coiled into little balls; or shreds of mucus with great numbers of entangled pus-corpuscles. The sputum should always be examined, both unstained and stained. A. UNSTAINED SPUTUM The particle selected for examination should be transferred to a clean slide, covered with a clean cover-glass, and examined with the two-thirds objective, followed by the one-sixth. It is convenient to handle the bits of sputum with a wooden toothpick, which may be burned when done with. The platinum wire used in bacteriologic work is less satisfactory because not usually stiff enough. The more important structures to be seen in unstained sputum are: elastic fibers, Curschmann's spirals, {27} Charcot-Leyden crystals, fibrinous casts, the ray fungus of actinomycosis, and molds. Pigmented cells, especially the so-called "heart-failure cells" (p. 43), are also best studied without staining (Plate II, Fig. 1). [Illustration: FIG. 4.--Elastic fibers from the sputum: _a_, Highly magnified; _b_, alveolar arrangement, less highly magnified (after Bizzozero).] 1. Elastic Fibers.--These are the elastic fibers of the pulmonary substance (Fig. 4). When found in the sputum, they always indicate destructive disease of the lungs, provided they do not come from the food, which is a not infrequent source. They are found most commonly in phthisis: rarely in other diseases. Advanced cases of tuberculosis often show great numbers, and, rarely, they may be found in early tuberculosis when the bacilli cannot be detected. In gangrene of the lung, where they would be expected, they are frequently not found, owing, probably, to the presence of a ferment which destroys them. {28} The fibers should be searched for with a two-thirds objective, although a one-sixth is needed to identify them with certainty. Under the one-sixth they appear as slender, highly refractive fibers with double contour and, often, curled or split ends. Frequently they are found in alveolar arrangement, retaining the original outline of the alveoli of the lung (Fig. 4, _b_). _Leptothrix buccalis_, which is a normal inhabitant of the mouth, may easily be mistaken for elastic tissue. It can be distinguished by running a little iodin solution under the cover-glass (see p. 37).