3 Traité de la Pneumonie.
Recently, Jürgensen has strongly advocated the infection theory of pneumonia, and has presented strong arguments in support of his opinions. Sturges of London and Cohnheim4 advocate the use of the term pneumonic fever, and the former gives a most interesting general comparison between it and the affections which he regards analogous to it. Careful pathological experiments have recently been made by Heidenhain, Sommerbrodt, Schuppel, and Klebs5 with a view to establish the germ-theory of pneumonia.
4 Leçons de Chir. méd., 1877, p. 17.
5 Arch. für experiment. Pathol., p. 420.
The literature of the past ten years is richer in the development of facts and experimental investigations than all the centuries that have preceded; and these recent experiments, combined with modern statistics and the results of the microscope in pathological histology, have given to croupous pneumonia a separate and distinct place in the list of pulmonary diseases.
MORBID ANATOMY.—Anatomically as well as clinically, there are three recognized stages in croupous pneumonia: 1, Stage of engorgement or congestion; 2, Stage of red hepatization; 3, Stage of gray hepatization, resolution, or purulent infiltration (suppuration).
It has been claimed that the stage of engorgement is preceded by a dry stage, or "stage of arterial injection," in which the lung-tissue is dry and of a bright-red color. It is evident that congestion of the minute branches of the pulmonary artery would not give to the lung-tissue a bright-red color, and if such a condition exists it must be due to injection of the bronchial vessels. It is by no means proven that such injection ever precedes pneumonic engorgement. In the stage of engorgement that portion of the lung which is involved in the pneumonic process does not collapse when the thoracic cavity is opened. The affected portion of lung is distended and firmer than normal lung-tissue, and when pressed upon crepitates less, often remaining indented after the pressure is removed. The lung is not entirely airless, for by pressure the air can be forced from one portion of it to another. Its color is darker than normal, usually being of a brownish-red or purple. There is an increase not only in its actual weight, but in its specific gravity. On section a thin, frothy, blood-stained serum exudes, and sometimes on pressure flows freely from the cut surface; occasionally this exudation is tenacious. When alcohol is added to this fluid, it coagulates into a granular, amorphous mass.
The capillaries around the air-cells are distended, and dark blood oozes from their divided ends. Occasionally, upon close examination, there may be seen beneath the pleura and between the air-sacs small points of blood-extravasation. A portion of lung in this stage, when placed in water, does not float as near the surface as healthy lung-tissue.
When examined with the microscope, the lumen of the alveoli are seen to be diminished by the encroachment of the varicosed and tortuous capillary vessels. As a rule, the air-sacs are uniformly dilated; some, however, may be collapsed—a condition probably due to pressure during the early period of the pneumonic process. The epithelia of the alveoli are swollen, and contain a granular protoplasm with free nuclei. The air-vesicles also contain exfoliated epithelial cells and white and red blood-corpuscles. The serum which escapes into the alveoli from the distended capillary vessels is the fluid in which these cell-elements float. Since the enlarged epithelia often suffer a division of their protoplasm, embryonic mono-nucleated cells are intermingled with the other elements. It is still a disputed question whether the bronchial or the pulmonary capillaries are the chief source of the pneumonic exudation.
Physiology teaches that lung-tissue is nourished by the blood in the ramifications of the bronchial arteries, and that the pulmonary capillaries are the passive media for the interchange of gases. Hence it is claimed that the bronchial capillaries only are implicated in the inflammatory process. Virchow has shown that the pneumonic process can be completely established in places where pulmonic capillaries cannot be traced on account of the plugging of a large branch of the pulmonary artery;6 yet even he admits that secondarily the pulmonary vessels have much to do in the inflammatory process.