When the examination is begun, the sputum should be spread out in a thin layer in a Petri dish, or, better, between two small plates of glass, like photographic plates. It may then be examined with the naked eye--best over a black background--or with a low power of the microscope. The portions most suitable for further examination may thus be easily selected. After an examination the sputum must be destroyed by heat or chemicals, and everything which has come in contact with it must be sterilized. The utmost care must be taken not to allow any of it to dry and become disseminated through the air. Examination of the sputum is most conveniently {25} considered under three heads: I. Physical examination. II. Microscopic examination. III. Characteristics of the sputum in various diseases. Chemic examination yields nothing of clinical importance. I. PHYSICAL EXAMINATION 1. Quantity.--The quantity expectorated in twenty-four hours varies greatly: it may be so slight as to be overlooked entirely in beginning tuberculosis; and it may be as much as 1000 c.c. in bronchiectasis. 2. Color.--Since the sputum ordinarily consists of varying proportions of mucus and pus, it may vary from a colorless, translucent mucus to an opaque, whitish or yellow, purulent mass. A yellowish-green is frequently seen in advanced phthisis. A red color usually indicates the presence of blood. Bright red blood, most commonly in streaks, is strongly suggestive of phthisis. It may be noted very early in the disease. A rusty red sputum is the rule in croupous pneumonia, and was at one time considered pathognomonic of the disease. "Prune-juice" sputum is said to be characteristic of "drunkard's pneumonia." A brown color, due to altered blood-pigment, follows hemorrhages from the lungs. Gray or black sputum is observed among those who work much in coal-dust, and is occasionally seen in smokers who "inhale." 3. Consistence.--According to their consistence, sputa are usually classified as serous, mucoid, purulent, seropurulent, mucopurulent, etc., which names explain themselves. As a rule, the more mucus and the less pus and serum a sputum contains, the more tenacious it is. {26} The rusty sputum of croupous pneumonia is extremely tenacious, so that the vessel in which it is contained may be inverted without spilling it. The same is true of the almost purely mucoid sputum ("sputum crudum") of beginning acute bronchitis, and of that which follows an attack of asthma. A purely serous sputum is fairly characteristic of edema of the lungs. II. MICROSCOPIC EXAMINATION