Lobular pneumonia usually begins in isolated groups of vesicles, being often determined by the presence in them of inflammatory products drawn from the small tubes with which they are in communication. On inspec tion of the lungs we see scattered nodules of consolidation of a reddish gray colour scattered over the surface. They vary in size from a small pea to a nut. Their consistence is friable, their substance smooth or faintly granular, and their circumference ill-defined. As the process advances, the nodules which were at first isolated become united at their borders so as to produce considerable tracts of consolidation ; and at the same time the solidified parts become firmer, dryer, and of a yellowish gray colour. In their centres we can sometimes see divided air-tubes filled with purulent matter.
The lung-tissue in which the nodules are embedded exhibits collapse, congestion, oedema, and emphysema in various stages and degrees. A certain amount of dilatation of vesicles is almost invariably present in the neighbourhood of collapsed portions of lung, and there is, moreover, an appreciable degree of cylindrical dilatation of all the minutes bronchi, especially of those portions which immediately adjoin the terminal alveoli. The walls of these tubes are excessively attenuated. The dilatation appears to be the consequence in some cases of accumulation of secretion. In others it is due to diminution of the respiratory surface, for plugging of seine tubes with mucus causes an increased rush of air to the parts which still remain pervious.
The consolidating matter itself consists in a very small degree of ex uded corpuscles, as in the case of croupous pneumonia. On examination the alveoli will be found to be stuffed with cells, but these are in great part derived from proliferation of the epithelial lining of the vesicles. Mixed up with these epithelial elements are leucocytes and much gelatinous mu cold matter—probably secretion from the inflamed bronchial mucous mem brane which has been drawn into the alveoli. In all cases of catarrhal pneumonia large quantities of thick puriform bronchial secretion are found filling the air-cells and plugging the finest tubes. When this is very copi ous the amount of epithelial cells is comparatively insignificant. Thus, some of the nodules of consolidation appear to be composed almost exclu sively of thick bronchial secretion ; and a microscopic examination shows very few proliferated cells and little change in the epithelial lining of the alveoli. In other parts the nodules are composed almost entirely of epi thelial elements, and the epithelium lining the alveolar walls is swollen, granular, and partially detached.
These lesions are found in both lungs ; and the process begins in the most depending part, i.e., in the lower lobes at the posterior aspect ; for gravitation greatly aids the passage into the cells of these parts of purulent secretion descending from the tubes. The extension of the inflammation laterally is always irregular, and the selection of the lobules for attack ap parently capricious ; for while some become consolidated, others in imme diate contact with them remain healthy or merely congested. The nodules and patches of solidification are at first isolated, but tend to coalesce, and in the latter period of the disease comparatively wide areas of consolida tion may be found.
The pleura in the neighbourhood of the spots of consolidation is red dened with points of ecchymosis, and adhering to it is often a little plastic lymph.
If the case do not terminate unfavourably, resolution usually ensues. A. process of fatty degeneration takes place in the contents of the alveoli. The consolidating material becomes softened down and is removed more or less rapidly by absorption and expectoration. The process of resolution often occupies some time even when the lung finally returns to a normal condition. Often, however, the process of fatty metamorphosis becomes arrested. The cells then atrophy and become caseous, and a chronic con solidation is left which forms one of the varieties of pulmonary phthisis. In other cases an indurative pneumonic process is set up which leads to a great development of fibroid tissue in the part. The walls of the air-tubes and the alveoli become thickened and indurated and the tubes dilated. This condition forms a special variety of lung disease which will be after wards described (see fibroid incluratiqn of the lung).
Symptoms. —Broncho-pneumonia is a secondary disease. Its symptoms are always preceded by those characteristic of a more or less severe pul monary catarrh. In weakly, ill-nourished children, especially if they are suffering from an attack of measles, a comparatively trifling catarrh will set up lobular inflammation of the lungs. In a robust child inflammation of the alveoli seldom ensues unless the preliminary catarrh has been long continued or very severe. When broucho-pneumonia follows an ordinary catarrh of the lungs, the disease usually runs a very acute and rapid. course and cominonly ends in death. When it arises in the course of an attack of measles or whooping-cough the complication is more subacute in charac ter and the proportion of recoveries is greater. Still, such cases tend to leave unabsorbed deposits in the lungs.