SPUTUM.—The material expectorated from the air-passages by the acts of hawking and coughing. In addition to the saliva from the mouth, it usually contains watery, slimy. or purulent matter, which has been excreted from the mucous membrane lining the respiratory passages. The sputum may contain also blood and fibrine, cells from the bronchial mucosa, crystals derived from the tissue fluids, elastic fibres from the lungs, foreign bodies (such as coal-dust, rust, etc.), and minute vegetable and animal organisms. If there is much mucus present in the sputum, the latter becomes tough, stringy, and sticky, and can he expectorated only with difficulty. The more pus it contains, the less tenacious the sputum will be. Dense masses of sputum, which contain no air, quickly sink in water ; but if air be present it floats on the surface, or adheres to the sides of the sputum cup.
The quantity of sputum expectorated varies in different diseases, and even in different stages of the same disease. As a rule, the amount increases when inflammatory processes in the air-passages undergo resolution. Dilata tion of the bronchi, pulmonary cavities, rupture of an encapsulated abscess in the lung, or the perforation of a purulent process from the pleural cavity into one of the bronchi, may all be accompanied by the discharge of large quantities of mucus. The colour also varies. If the expectoration consists largely of mucus, it has a whitish colour ; but if a smaller or larger amount of pus be present it assumes a yellow or a yellowish-green tinge. Grey or
black discoloration points to admixture of dust or soot, while a reddish tinge indicates the presence of blood.
A diagnosis of the prevailing disease can only in exceptional cases be made from an examination of the sputum. The latter must be regarded as merely one of a number of symptoms ; and it does not do away with 'the necessity of making a careful inspection of the lungs. Some forms of sputum, however, are more or less characteristic of the disease present. A slimy, whitish-grey expectoration is indicative of bronchial catarrh ; rust-stained sputum is symptomatic of pneumonia ; expectoration which, on standing, separates into three, layers, is characteristic of pulmonary gangrene ; and a purulent sputum, which separates into coin-like masses as it sinks to the bottom of the sputum-cup, is indicative of cavities in the lung. A foul odour indicates that a disintegrating process is going on in the lungs. The microscopical examination of the sputum is of great importance. The presence of the tubercle-bacilli establishes a diagnosis of pulmonary tuber culosis ; and the increase or decrease in their number affords a fairly good method of estimating whether the disease is improving or getting worse. The small cysts of the echinococci, or their remnants, are rarely found in expectorated matter. For the expectoration or coughing of blood, see