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.
[Illustration:
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.
]
[Illustration:
FIG. XLIII. THE ALVEOLAR WALLS ARE THIN AND THE EXUDATE OF RED BLOOD
CELLS AND DESQUAMATED EPITHELIUM IS IN PART HYALINIZED.
]
The advent of red blood cells where grossly the exudate is red can
hardly be explained by the simple process of diapedesis. Indeed, there
is ample evidence that they escape by rhexis through lesions of the
vascular wall. This phenomenon cannot be demonstrated in areas where a
compact mass of red cells obliterates the alveolar space (Fig. XXV), but
in the less firmly consolidated alveoli where red blood cells
predominate (Fig. XXVI) the picture of the alveolar wall is very
instructive. The capillaries may be prominent and contain red cells
almost exclusively. Often the epithelium of the air space is exfoliated
so that there is nothing to minimize the prominence of the engorged
vessels. These capillaries, covered by such a delicate wall that rupture
seems imminent, may protrude like saccular aneurysms (101) into the
alveolar space (Fig. XXVI). In all probability, these sacs do rupture
and this result would be one explanation for the escape of large numbers
of red blood cells. In several instances such a picture was encountered,
where with little reaction at the point of rupture, red cells within the
vessel were continuous with an accumulation of similar cells in the
alveolus. Further evidence for such rupture is offered where the vessel
is collapsed. Here there is accumulation of polymorphonuclear leucocytes
in the area of destruction in contrast to the well preserved red
corpuscles in the remainder of the vessel (Fig. XXVI). The above
pictures may be utilized in the interpretation of the outspoken foci of
red hepatization which may assume infarct-like proportions. As has been
said, it is impossible to conceive that these hemorrhagic areas where
the alveoli are packed with red cells ever change to a grey type of
consolidation. Consequently, it seems more probable that the color of
red hepatization in the usual types of pneumonia depends upon the marked
engorgement of the vessels seen through a relatively acellular,
transparent, serofibrinous, alveolar mass and not upon the number of red
cells in the exudate.