In considering the causes which tend to produce this condition they seem to resolve themselves into the following: 1st. the exist ence of mucus in the bronchi, which is more liable to produce obstruction according as it is more thick and viscid; and 2ndly, weakness or inefficiency of the respiratory power; 3rdiy inability to cough and expectorate. Of these conditions, the first must be considered as the exciting cause, the others as predis posing, co-operating with the first, but in capable, without it, of producing collapse.* With bronchitic collapse of the lung is ahnost always associated emphysema of the unaffected portions of the same lung (Gaird ner).
Infianznzation of the mucous nzembrane of the bronchi produces changes which are denoted by redness and tumidity of the tissue, a secretion of muco-serum, purulent mucus, or pus, according to the stage and intensity of the inflammation.
This latter is the condition of supezficial suppuration. The swelling of the mucous membrane and sub-mucous tissue, which as sumes the form of watery infiltration into the The preceding distribution of the morbid conditions of the air passages may be advan tageously methodised under two heads : first, those of the bronchi (as defined in the account of their normal anatomy) ; secondly, those of the lungs.
The bronchi are liable to several forms of inflammation : Collapse of the lungs should be considered, pathologically, as rightly ranking under the denomination of the diseases of the bronchi.
The various forms of asthma, and hooping cough, belong to this species.* The bronchi are subject to two forms of dilatation. In the first, a tube is uniformly dilated at every part of its circumference. In the second, the dilatation is saccular. The areolar tissue, being accumulated at individual spots, is important and worthy of great atten tion, on account of the facility with which it interferes with the calibre of the tubes.
Chronic inflammation of the bronchial mem brane gives rise, especially in parts abounding in glands, to glandular hypertrophy, mucous polypi, epithelial growths, sponzy and velvety thickening, relaxation of the muscular and fibrous elements, follicular ulceration, &c.
The pathological conditions of the broncho pulmonary mucous membrane differ in no respect from those of any other membrane of this class.
In plastic or exudative bronchitis are cha racterised by a morbid action of a croupous nature.
In bronchial croup the tubular exudations from the larger bronchi present a calibre in versely proportional to their thickness, and those thrown off from the finer ramifications occur as solid cylinders.
Asthmatic affections may either have their exciting cause in the lungs or in the condition of some remote organ. They partake of a nervous and muscular character, and are frequently caused by a collapse of a portion of the lung. The collapsed part operates as an excitor of the muscular spasm.
English pathologists recognise the follow ing forms of disease proper to the parenchyma of the lungs :—Pneunzonia, or inflammation of the cell-tissue of the organ ; gangrene ; lwenzorrhag,e ; wdenta ; emphysema ; phthisis ; cancer.
Inflammation of the vesicular tissue of the lungs is marked by the exudation of the co loured elements of the blood. This fact was once supposed to prove the absence of epi thelium in the air-cells. This inference is erroneous.
Inflammation of the lung is divided into three stages, according to the consistency- or physical condition of the exuded product. The first is that of engorgement ; the second is that of hepatisation ; the third is that of grey hepatisation.
Gangrene of the lungs occurs under two anatomical forms, the diffused and the cir cumscribed.
Cancer of the lung, most commonly of the encephaloid species, occurs in the forms of secondary nodules and primary infiltration, accompanied or not by tuberous formation on either maliastinuni about the main right bronchus (Walsh).
The anatomical changes which occur in the lungs in phthisis are referrible to three main stages, corresponding habitually to certain varieties in the symptoms, and always to modifications in the physical signs. The first stage is that of deposition and induration ; the second that of softening; the third that of excavation.
The exact scat of pulmonary tubercle has proved, from the dawn of pathology to the present time, a controverted point. The question is whether the deposit of the morbid product occurs first on the free surface of the air-vessels into the substance of their walls, or between them into a supposed inter vesicular tissue. From Morton and Bayle to Rokitansky and Lebert, advocates for each of these "seats of election" have contended in turn. The free or aerial surface of the air-cells is now the commonly accepted si tuation of the tuberculous deposit.
The nature of the tuberculous matter is not less disputed ; witness the following defi nitions : — Tubercle is a specific exudation (Ancell). Tubercle is a degraded condition of the nutritive material (Dr. C. J. B. Williams). Tubercle is composed of the products of inflammation (Reinhardt).
Tubercle is composed of the dead-tissue elements (Henle).
Tubercles themselves consist of abnormal epithelial cells (Dr. W. Addison).
Tubercles are composed of metamorphosed organised elements ; a metamorphosis co ordinate with the fatty and the waxy de generations (Virchow).
Tubercle is a product secreted from the blood by the epithelium lining the air-cells (Schroeder Van der Kolk*).
The mechanisnz of emphysema is still sub judice. Some authors, with Laennec, ex plain it on the supposition that the walls of the air-vesicles yield under the force of the air when the expiratory current is impeded. Another class of writers attribute it to an excess in the inspiratory force. Mr. Rainey contends that the parietes of the air-cells suffer a change of structure by fatty dege neration, and that this change stands to em physema in the relation of a causal condition. Dr. Gairdner affirms that emphysema of one portion of the lung cannot occur unless a collapse has happened in another part. Em physema fills up pneumatically the space lost by the collapse, and no more. The chest can only be filled; it cannot be inflated beyond a given inspiratory limit. The air passages of the emphysematous portions are free, not obstructed. If already the cavity of the thorax be uniformly filled, it is certain that emphysema is rendered physically im possible. Emphysema is plenunz counter balancing collapse—a vacuum.
lt is yet by no means determined to what extent, if at all, the shedding or desquamation of the epithelium of the air-passages takes place in disease.
(Thomas Williams.)