DISEASES OF THE LUNGS.
Inflammation of the Lungs (Pneumonia). —This form of inflammation of the respiratory organs attacks specially the air-cells of the lungs, the lung substance itself. A description of the regular form will enable one to under stand the nature of the disease.
The blood-vessels of the affected part of the lung are engorged with blood, specially the blood-vessels in the walls of the air-cells (p. 344), and also the vessels in the walls of the passages and fine bronchial tubes communi cating with them. The pressure of blood in the vessels causes fluid (serum) to ooze from them and enter the cells and passages. As the inflammation continues, besides serum, other parts of the blood escape, namely, fibrin and also blood corpuscles (p. 292). This mate rial completely expels the air from the affected portion of the lung, which thus becomes heavy and solid, and, being capable of clotting, the material forms a gelatinous mass in the air cells. In the next stage of the disease this in flammatory material breaks down into matter, which is more liquid, and may be expelled from the air cavities and cells. As it is gra dually expelled, coughed up, and spat out, the air spaces become unloaded, and air begins again to pass into them. If the case has pur sued an entirely favourable course, the in flamed portion of lung will, after some time, be restored to its former activity and useful ness, with little trace of the serious changes it has passed through.
There are thus three stages in the progress of the disease. The first stage is that of con gestion or engorgement, the second is called that of red hepatisation, from Greek, hepar, the liver, because the solidified part of the lung looks like a piece of liver, being red in colour owing to colouring matter of the blood ; the third stage is that of gray hepatisation, the change in colour being due to breaking down of the contents of the air-cells.
Inflammation attacks the right lung twice as often as the left; and generally it is the lower parts of the lung that suffer, both lungs not often being inflamed at the same time. In the typical form a whole lobe is the seat of the inflammation, the lower lobe usually, but the upper lobes may also be affected. Hence the term lobar pneumonia has been used to distinguish from lobular pneumonia, which attacks the lungs in patches, separated by healthy lung tissue, and is more common among young children than among adults. The lattem form is also called catarrhal pneumonia, since it is frequently a termination of catarrh or cold in the chest. It may also be stated that lobar
pneumonia is also called croupous, because of. the fibrinous material poured into the air-cells that characterizes the typical case. In most cases of pneumonia there is some amount of bronchitis (p. 363), owing to the affection of the smaller bronchial tubes. There may be also pleurisy (p. 359), that part of the pleura which is in contact with the inflamed portion of lung suffering with it. When the pleurisy is marked the doubled affection is called pleuro-pneumonia.
The pneumonia may not end, however, so favourably as has been supposed. A fatal termination may be due to the extent and violence of the attack, or to weakness, the heart being specially liable to fail because of the extra work thrown upon it in driving the blood through the obstructed lung. A chronic condition may be set up, which is considered later. In some cases, comparatively few, and only in those of very weakened constitutions, who suffer probably from other disease, the pneumonia ends in a part of the lung dying, and breaking down into fetid matter. This constitutes gangrene of the lung.
The chief cause of the disease is exposure to cold, and specially to sudden considerable variations of temperature, so that it is common in spring. It may, however, arise from exten sion of inflammation from the pleurie or the bronchial tubes. Thus a common cold, neglected, may end in pneumonia. Other inflammations— those attending whooping-cough, measles, diph theria, &c.—may occasion it, while it may arise in the course of other diseases, such as those of the heart, kidney, &c. Inhalation of irritat ing vapours or particles is another cause. For example, the solid particles inhaled by miners, knife-grinders, &c., are capable of producing it. Drinking a large quantity of cold water in an overheated condition of the body, by driving the blood from the organs of the belly to the lungs, may bring on an attack. Pneumonia, however, has come to be regarded as a disease due to an organism of the micrococcus form (see p. 495), the pneumococcus of Friedhinder, which is found in the spit in cases of the dis ease, and it seems quite certain that in some circumstances of an insanitary kind the disease is infective. It may be that the chill, or other cause to which the disease used to be attributed, acts only as a predisposing cause, the organism being able to flourish in and take possession of the temporarily depressed lung.