This section is from the book "The Home Hand-Book of Domestic Hygiene and Rational Medicine. Volume 2.", by J. H. Kellogg, M.D.. Also available from Amazon: The Home Hand-Book of Domestic Hygiene and Rational Medicine, Volume 2 .

Much can be learned of the condition of the lungs from an examination of the matters expectorated, or what is technically known as the sputum. The chief points of interest in relation to the sputum are its consistence, quantity, odor, color, and constituents.

Consistence of Sputum

The density of expectorated matter varies greatly. It may be tough or tenacious or a limpid fluid. When very firm, it consists almost wholly of mucus, and is an indication of a high degree of irritability of the mucous membrane. This kind of expectoration generally has the form of little round masses which are raised with great difficulty. When the sputum comes from enlarged bronchial tubes, or from cavities in a consumptive lung, it contains some pus and is less firm. The rounded masses are then somewhat flattened, but retain their form for some time after expectoration. Opaque fluid sputum is usually pus. It occurs in bad forms of bronchitis of long standing, in abscesses of the lung, and in cases of empyema in which an opening into the air passages allows the pus in the pleural cavity to escape into the lung. It often occurs also in the advanced stages of consumption, at intervals. A clear, fluid expectoration indicates oedema of the lung from passive congestion. Frothy mucus, or that which contains much air, floats upon water, while that of greater consistence sinks. When the sputum sinks and retains its rounded form, it is generally supposed to indicate the presence of a cavity in the chest; but the evidence is by no means positive, as the same kind of sputum may occur in bronchial catarrh.

Quantity of Sputum

The quantity of expectoration is not very significant, since it may be quite abundant in very mild cases, and scanty in the most severe ones. As a general rule, especially in whooping cough and acute bronchitis, the increase in the quantity of sputum and the disappearance of the difficulty in raising it, occur at the same time. When the sputum becomes scanty, the violence of the cough greatly increases. The sudden cessation of expectoration in a case in which it has been quite copious is a very bad symptom, especially if the patient shows signs of weakness. This is one of the forerunners of death in consumption. A very copious expectoration, as of several tablespoonfuls at a single act of coughing, is indicative of a pulmonary abscess, or of empyema if it occurs but once, and suddenly, If habitual, occurring perhaps every morning, it is evidence of dilatation of the bronchial tubes.

Odor of Sputum

The odor of the sputum is not usually marked; but it becomes very fetid when it is long retained in the lung before expectoration, as in enlargement of the bronchial tubes in cases of chronic bronchitis, in abscess of the lungs, in the putrid form of bronchitis, and in consumptive cases with cavities. The odor is extremely bad in cases of gangrene, when the lung substance is undergoing rapid destruction.

Color of Sputum

Red sputum of course indicates the presence of blood. When the blood is not expectorated at once, but becomes mixed with mucus, the sputum will be likely to be reddish brown or very slightly tinged with red. The rusty sputum seen in pneumonia owes its color to the presence of blood. In some cases, after blood has been retained for some time, it gives to the sputum a yellow or greenish color. These colors are generally due, however, to the presence of pus. The occurrence of jaundice in a person who is expectorating freely usually causes the sputum to assume a yellow or green color. The sputum is often colored by dust inhaled, as by coal dust in stokers, miners, and those who labor in coal.