Another striking feature of the inflammatory process in this disease is the extensive hemorrhagic exudate expressed clinically in the fresh, red blood of the abundant sputum. In the tissues the blood is always fairly well preserved. It may be scattered diffusely through the cellular exudate (Fig. XXIV) or so abundantly that the area resembles an infarct (Fig. XXV). These hemorrhagic foci, which vary considerably in size, are found not only in the cases that terminate fatally within a few days, but may occur at any time during the acute manifestation of the disease. They are an exaggerated form of red hepatization and it is difficult to see how such red foci could ever change to areas of grey pneumonia. It is a widely accepted statement, in textbooks of Pathology at least, that the stage of red hepatization in pneumonia follows the period of engorgement and precedes the grey form. This interpretation is open to question concerning the lesions that are encountered in influenza, as well as in those that are seen after gas inhalation. Unquestionably, in the stage of engorgement the lung has a red appearance, enhanced by the acellular, serofibrinous exudate in the alveoli through which the greatly congested vessels are seen. At this stage, the lung has a translucency on gross examination, which is not the case when the cellular content of the alveoli is increased. This picture is not the one spoken of most commonly as red hepatization; for, although it appears as a relatively red lung in the gross, difficulty is encountered in its histological correlation, for the exudate is composed, not of red cells, but largely of serum and fibrin. The red color may persist even when numerous polymorphonuclear leucocytes and desquamated alveolar wall cells are within the alveoli, the walls of which are markedly engorged. Later, as the circulation in the pneumonic zone is impaired, the alveolar exudate determines the tone of the gross color, and a considerable number of red blood cells may be overshadowed by the larger percentage of white ones.
FIG. XLII. AUTOPSY NO. 133. IS A MUCH LATER STAGE OF THE PROCESS SHOWN IN FIGURE XXXI. ASSOCIATED WITH THE ENCAPSULATED BRONCHIOLAR AND PERIBRONCHIOLAR ABSCESS, THERE IS A DIFFUSE ORGANIZATION OF THE EXUDATE IN THE SURROUNDING ALVEOLI. ]