The absence of cellular elements in the alveolar exudate is frequently
observed in influenzal pneumonia (Figs. XXI, XXII, XXIII). This picture
has been reproduced experimentally in animals which have been rendered
aplastic with benzol, especially with reference to their myeloid
elements (160). Pneumonia produced by intratracheal insufflation is more
rapidly fatal in aplastic animals, and it is conceivable that the
absence of cellular reaction is an explanation for the lack of
resistance demonstrated by the high mortality of influenzal pneumonia.
Frequently the fibrinoserous mass scattered diffusely throughout the
lung is rich in bacteria. In the absence of cells of the
polymorphonuclear series, the bacterial development seems to be
unrestricted. The aplastic exudate is associated clinically with an
absence of a myeloid reaction in the peripheral circulation. The
leucocytic count may be definitely decreased, even though the tissues
have been invaded by pyogenic organisms to which the usual response is a
definite leucocytosis. The only explanation is that the myeloid
structures have been injured, probably by the unknown virus of the
disease.