In all the fatal cases of influenza which came to autopsy, and this has been the experience of others, the respiratory lesions, as indicated above, occupy the foreground. Indeed, compared with other types of respiratory disease, the lung involvement is so great that expression of the disease need not be sought elsewhere to explain the cause of death. However, there are general systemic changes which, even though quantitatively inconstant, are sufficiently common and widespread to support the view that the disease is a systemic one. The lesions of the hematopoietic organs and those of the vascular system are the most important and will now be taken up. A. LESIONS OF THE HEMATOPOIETIC SYSTEM There is ample evidence that both the lymphadenoid and myeloid tissues of the body are affected. The lymph glands at the hilum of the lung naturally are involved with the extensive pulmonary changes. Also, a similar change may be found in distant nodes, perhaps associated with drainage from focal lesions or perhaps brought about by general intoxication. The myeloid involvement is unassociated with focal lesions and finds its early expression in the equation of the white blood cells of the peripheral blood. The two groups of changes, those involving the lymphadenoid and those of the myeloid structures, should be discussed separately. _Lymphadenoid Tissues._ By far the most extensive lesions are encountered in the lymph glands of the lung and its hilum, and from here the mediastinal and deep nodes along the trachea are affected to a greater or lesser extent. The glands are very large and succulent (2, 157, 162, etc.). Very frequently, indeed, they are hemorrhagic on cross section (34, 108) (Fig. XXXVII), and there exudes a sanguinous fluid, usually thin and syrupy in character. The cut surface projects slightly, and the edge of the gland everts. The architecture is often obscured by hemorrhage—a diffuse red color—but very frequently near the periphery, translucent or more opaque, yellowish points are visible. Rarely, larger, opaque, yellow foci are found in the gland; these may be softened and purulent in exceptional cases (2, 47, 157).