We include here those conditions in which the lung tissue is the seat of a simple chronic inflammation, without anything of a tubercular or other specific nature. The simplest cases are those in which an acute pneumonia, instead of resolving, passes into a chronic condition. But there seem to be cases also in which a pneumonia is chronic from the outset. This is the case commonly in old persons, and it may therefore be said that senile pneumonia is included under the present head. To a certain extent the same is true of pneumonia in drunkards and in debilitated persons, especially when it affects the apex of the lung. In addition to that we have a very important group in which chronic inflammation is set up by the inhalation of irritating solid particles, as among potters, stone-hewers, etc. (See further on).
The chronic inflammation here, as in other organs, is chiefly characterized by a new-formation of connective tissue, so that Induration of the lung is the result. In this view of it the terms chronic interstitial pneumonia, cirrhosis, sclerosis, are sometimes used as being virtually of the same meaning as chronic pneumonia. But here it is necessary to distinguish very carefully. We shall see afterwards that there is a form of tuberculosis of the lung commonly called fibroid phthisis, in which a great new-formation of connective tissue occurs. It is of importance to note that while fibroid phthisis leads to great shrinking and contortion of the lung, there is little of this effect in most cases of chronic pneumonia, the conditions in this respect differing from those in interstitial inflammation of the liver and kidneys.
The naked-eye appearances presented by the lung in cases of acute pneumonia which have had a prolonged course and have become chronic are not unlike those of the lung in the stage of grey hepatization. The disease is generally confined to one lung, and may affect only a portion of it. The lung is bulky and dense, and feels solid to the touch. When cut into, the solid lung has usually a grey colour, although sometimes with a tint of red, but it has a smoother cut surface than that in hepatization, and the tissue is much tougher. To this condition the name Iron-grey induration may be aptly applied.
Under the microscope the conditions are such as are indicated in Fig. 362. The walls of the alveoli are greatly thickened by fibrous tissue, which largely encroaches on the alveoli, the epithelium of which is preserved, and sometimes occupies their interior. When it is considered that the lung as a whole is not reduced in bulk, and that the alveoli are in great part empty, then the overgrowth of connective tissue will be understood to be very great. Along with the interstitial new-formation there is commonly thickening and adhesion of the pleura. In some cases there is a very striking appearance as if the fibrinous plugs in the alveoli in acute pneumonia were being eaten into and replaced by connective tissue. There are obvious masses of connective tissue inside the alveoli, sometimes distinctly pedunculated These have arisen in a. manner similar to that in which a thrombus becomes organized, the new formed tissue moulding itself on the fibrinous plug.
Fig. 362. - Chronic pneumonia. The connective tissue is greatly increased, and the alveoli (a, a, a) are represented by contracted spaces lined with well-formed epithelium. The epithelium here is much more distinct than in the normal alveoli, x 350.
This appearance establishes the fact that chronic pneumonia sometimes develops out of acute, a view which has been questioned.
In some cases the new-formed connective tissue takes on a cicatricial character and by its contraction destroys and contorts the proper lung tissue. Just as in the case of cirrhosis of the liver, there is here an atrophy of the normal structure and a tendency in the organ to shrink. This leads to dilatation of the bronchi on principles already enunciated, so that Bronchiectasis is a prominent feature in advanced cases of this kind. The bronchial secretion may stagnate in the dilated bronchi and decompose; the irritation of the decomposing juices sometimes causes ulceration, and ragged cavities may thus form, so that the condition may come to resemble phthisis pulmonalis.
LAennec, Traite d'auscult. med., 1819; Rokitansky, Lehrb. d. path. Anat., iii., 1861; Stokes, Dis. of chest, 1837; Friedlander, Ueber Lungenentz., 1873; Jurgensen, in Ziemssen's Handb., 2nd ed., 1882, and Volkmann's Lectures (Syd. Soc. transl.'), 1876; Gairdner, Clin. Med., 1862; Sturges. Nat. hist, and relations of Pneum., 1876; Collective Invest. Record, vol. ii., 1884; Hirsch, Geograph. und histor. Path., 1886, iii., 125; Eussell, Peculiar outbreak of feb. disease, 1888; Strain, (Epidemic pneumonia) Glasg. Med. Jour., xxviii., 331; Leyden, (Abscess and gangrene) Volkmann's Samml., Nos. cxiv. and cxv., 1877; Auld, Lancet, 1890 and 1891; Sturges and Coupland, Nat. hist, and relations of Pneum., 1890.