The lungs of all adults have mOre or less of a grey colour from the existence of a black pigment in the lung tissue. This pigment is absent from the lungs of children, and is undoubtedly the dust inhaled with the inspired air. The air of all confined spaces, such as rooms, contains in suspension finely divided particles, particularly in cities where coal is burnt extensively, and this attains its maximum in the black fogs of such cities as London and Glasgow. The particles of dust inhaled with the air are for the most part caught by the mucus with which the surface of the bronchial tubes is moistened, and as the ciliated epithelium plays in the direction towards the larynx, the dust-laden mucus is carried upwards to the larynx, where it is either expectorated or swallowed. No doubt when the air is unusually laden with dust the mucous secretion is increased, and those who live in cities know that in foggy weather a considerable mass of black mucus is brought up from the larynx in the morning, the busy cilia having swept it thither during the hours of sleep.
But some of the dust penetrates beyond the reach of those scavengers and passes into the lung alveoli, where it lodges. From the lung alveoli it penetrates into the lung tissue. It is to be remembered that the structure of the alveolus is somewhat like that of a serous membrane. There is a single layer of epithelium, and stomata or pseudo-stomata have been described. The dust particles penetrate through or between the epithelial cells and emerge into the lymph spaces of the alveolar wall. Having entered the lymphatic system of the lung, the dust is carried into all the communicating channels of that system, and is partially deposited and retained as it goes by the connective-tissue cells. In this way a kind of pigmentation of the entire lymphatic system of the lung is obtained, which for demonstration may serve the purposes of an injection of that system. In this conveyance of the dust particles the leucocytes which are always present in the lymphatic spaces probably play an important part. The parts pigmented are, the walls of the alveoli, the interstitial connective tissue, especially that around the pulmonary artery and the bronchi, and the subpleural tissue, which is often definitely demarcated from the pleura proper by the pigmentation. The pigment is also carried to the bronchial glands at the root of the lungs, which are more or less blackened. This pigment is a carbonaceous material consisting mostly of round particles, and is to a great extent the soot of coal.
Fig. 377. - Prom a potter's lung, a, bronchus compressed and narrowed; b, two of its cartilages; c, c, condensed and pigmented lung tissue; d, lung alveoli, stretched and enlarged, some with pigment in them; f, lung alveoli emphysematous, x 8.
While the light dust of the air, reaching the lungs in small quantities, does comparatively little harm, damage may be done when large quantities of dust of a specially irritating character reach the lungs. Hence a distinct class of diseases has been distinguished as due to inhaled dust.
Diseases due to inhaled dust. Pneumoconiosis, Fneumonoconiosis.
This subject has been very fully worked out in this country by Greenhow, and in Germany by Zenker and Merkel. The results of the inhalation depend largely on the mechanical character of the dust. If it be heavy and composed of sharp angular particles, then it is more irritating than if it be light and composed of rounded pieces.
The particles entering the lung tissue in the manner mentioned above act as foreign bodies and set up a chronic inflammation. There is great new-formation of connective tissue, as in chronic interstitial pneumonia, and great shrinking of the tissue, so that considerable deformity of the lung may occur. As the irritant finds access by the air passages the lesion in its earlier stages concentrates itself around the bronchi. This is shown in Fig. 377, in which it is seen also that the lung alveoli are subject to great contortion (at d), and that in the neighbourhood they are liable to emphysema (at f).
The dust, whatever its kind, may be visible in the midst of the lesion in the lung. It was the observation, by Zenker, of a red pigmentation of the lung in workers with the red oxide of iron, which furnished an absolute demonstration that the dust actually finds its way into the lung tissue. We may find in the lung, coal dust, the dust of potter's clay, soot from smoky lamps, stone dust, metal dust, and dust composed of cotton or woollen fibre. In Fig. 378 a collection of silicious particles from the lung of a worker in the pottery is shown.
Fig. 378. - Silicious particles in potter's lung, x 340.
Fig. 379. - Part of the contents of a lung alveolus in anthracosis. Black particles are seen, some angular and others rounded. The large catarrhal cells contain many particles, x 350.
A peculiar feature in almost all cases of disease from inhalation of dust is the presence of an excess of Black pigment in the lung. In some cases the inhaled dust is black, so that a condition of anthracosis is brought about. But even when the dust is not black, as in the potter's lung, the affected districts of lung are deeply pigmented. The reason of this is not quite apparent.
Various names are given to the forms of lesion according to the kind of dust inhaled.
The Coal-miner's lung has an almost coal-black colour, and when incised it yields a black juice which stains the hand. The dust here is finely divided coal and the soot from the smoky lamps used in mines. The pigment is in the connective tissue, but it is often present also in the lung alveoli, where it may be taken into the substance of catarrhal cells (see Fig. 379). There is not usually much induration of the coal-miner's lung, as the dust is not physically very irritating. The term Anthracosis is given here owing to the extremely black appearance presented. An exceedingly well-marked example of this condition was recently observed in the lungs of a manufacturer of boot-blacking.
Coal miners are subject to catarrh, and the expectoration is usually stained so as to form the Black spit. It is noteworthy that on a recurrence of catarrh, even years after the patient has ceased working in the pits, the black spit may return. The pigment stored up in the lung tissue returns to the alveoli and bronchi. This would indicate that a bronchial catarrh goes deeper than the mucous membrane. The agents in the return of the pigment are the leucocytes.
Potter's phthisis is a term used for a very frequent form of disease amongst potters. . The dust here, consisting of heavy angular particles, seems very irritating, and excites much chronic inflammation.
Stone-mason's lung resembles the potter's form, as does also knife-grinder's disease.
The connection of these forms of disease with phthisis is a point of some importance. A true tuberculosis may possibly be induced by the inhalation of irritating dust. There is, however, little evidence of that, and undoubtedly the great majority of cases of lung disease from inhalation of dust are quite different from cases of phthisis. There is no formation of tubercles, no caseation, seldom any formation of cavities, although these sometimes form by bronchiectasis. There is also the important clinical difference that persons affected with such diseases do not suffer in their general health as do tubercular patients. There is little or no fever, and the patients generally work on for many years till the dyspnoea incapacitates them (Greenhow, Coats).
Gregory and Christison, Edin. Med. Jour., xxxvi., 389, 1831; Hamilton and Graham, ibid., xliii., 297, 1834; Thomson, Med. chir. trans., 1840, xx. and xxi.; Zenker, Deutsch. Arch. f. klin. Med., ii., 1866, and xxii., 1878; Arlidge, On the diseases prevalent among potters, Social Science Cong., 1871; also Allbutt's System of Medicine, v., 1898; Greenhow, Path, trans., 1866 to 1869; Coats, in Lect. to pract., 1888, p. 150; Catalogue, Path. Museum, West Infirmary.