Pneumonia, or Inflammation of the Lungs, is the name applied (with the necessary qualification) to a number of distinct pathological conditions. The catarrhal inflammation of Bronchitis (q.v.) may extend to the alveoli of the lungs, producing scattered patches of catarrhal pneumonia. The inflammatory changes in the lungs in consumption, including interstitial pneumonia, or cirrhosis of the lungs; in a few cases of syphilis; in wounds and injuries of the chest; in pyæmia; in the last stage of many exhausting diseases, all come under this head. But the most important form, to which the present discussion will be restricted, is that variously called acute, idiopathic, lobar, or croupous pneumonia, and is one of the most striking and definite of familiar diseases.
The changes occurring in an affected portion of lung are described in three stages. (1) Congestion: the lung-tissue still contains air, though less than in health, and is gorged with blood. (2) Red hepatization: the lung-tissue is solid like liver (hence the name), and is much more friable than in health; it still contains much blood, but no air, as the vesicles are completely filled with firm exudation, consisting of fibrinous material, mixed with leucocytes and red blood-corpuscles. (3) Gray hepatization: the tissue is still more friable and of a grayish colour, containing now little blood or blood pigment; the exudation has become much softer, as the fibrinous material has disappeared, and it oozes in part from the cut surface as a purulent fluid. It is doubtful whether recovery can take place when this third stage has been reached. When the surface of the lung is affected Pleurisy (q.v.) is always present as well as pneumonia.
The inflammation never attacks the whole of both lungs at once; the right is more often affected than the left, and the lower part than the upper. A whole lobe, or a large part of it, usually suffers; sometimes more than one.
The disease generally begins suddenly with a severe rigor or shivering-fit, and the temperature rises rapidly—usually to 103°–105° F. The pulse and respirations are both quickened, but the latter much more in proportion than in most other diseases, a most important indication of the nature of the case: instead of the usual ratio (about 4 pulse-beats to 1 respiration), the proportion becomes 3 or 2 to 1. All the usual signs of fever are present; but the patient's face presents a characteristic dusky flush; there is frequently severe pain in the affected part of the chest, and usually more or less cough, painful, but short, and suppressed as far as possible. In most cases after a few days the spit becomes very viscid and tenacious, and assumes a rusty tinge; this appearance is almost sufficient by itself to show the nature of the disease; but spit as well as cough may be absent altogether. The physical signs of the disease are very distinct. There is dullness on percussion over the affected area; and on auscultation marked and very characteristic changes in the breath-sounds. But if the inflammatory process happen not to reach a portion of the lung in contact with the chest-wall it may be impossible to detect anything abnormal.
It is always a serious disease; but the great majority of cases do recover. The circumstances which make it most alarming are the presence of other disease, especially of the heart or kidneys; previous habits of intemperance; and advanced age, as it is much less fatal in youth and middle life than after the age of sixty. Yet sometimes even cases apparently far from hopeful ultimately do well.
In favourable cases the fever usually terminates very rapidly, by crisis, as it is termed; in a few hours the temperature falls five or seven degrees, and the patient's discomfort becomes correspondingly relieved. In a very large proportion of cases this takes place between the sixth and the eighth day; but it may occur earlier, or it may be delayed to the fourteenth. After this has taken place the exudation in the affected portion of lung is gradually expectorated and absorbed, and as a rule perfect recovery takes place.
In a considerable number of cases pneumonia seems to be brought on by exposure to cold or wet. But in the majority no such cause can be traced. Only in very exceptional instances does it seem to be infectious; but epidemics on a small scale are of not infrequent occurrence, and sometimes assume large proportions. These facts, among others, have led many observers to believe that acute pneumonia ought really to be classed not with local inflammations, but with specific fevers; and that the inflammation in the lung has the same relation to the disease as the ulcers in the intestines to typhoid fever, or the inflamed throat to scarlet fever. In 1882 Friedländer described a form of micrococcus as occurring in the lungs in pneumonia. But it is doubtful whether it is always present in this disease, and it is sometimes found in other conditions. It must at present be regarded as an open question whether it is really a simple inflammation, with accompanying febrile disturbance, or a disease analogous to the infectious fevers, with a special local manifestation in the lungs.
The recognised treatment of pneumonia passed through curiously varied phases during the 19th century. Free and repeated bleedings, with extensive use of mercury, in vogue during the earlier decades, were superseded about the middle of the century by equally extensive administration of alcoholic stimulants. But it was gradually discovered that many cases recover perfectly with no other treatment than careful nursing; and the usual practice in recent times has been to assign to drugs only a subordinate place. Rest in bed in the recumbent position; a plentiful supply of fluid nourishment; light poultices, or a thick layer of cotton-wool, over the affected part, are often all that is necessary in a young and healthy subject. Severe pain may be combated by mustard poultices, blistering, or leeching; or it may require anodynes for its relief; sleeplessness, excessive rise of temperature, troublesome cough, or aggravation of any other symptom may require special treatment. The danger most to be feared in this disease, however, is generally weakness of the heart; and to patients of feeble constitution or advanced age stimulants—digitalis, ammonia, alcohol, &c.—are usually administered, often in large and frequent doses. See Sturges and Coupland, History and Relations of Pneumonia (2d ed. 1890).