═════════════════════════════╤═════════════╤═════════════╤═════════════ │ │ NO. WITH │PER CENT WITH │ NO. OF │ HEMOLYTIC │ HEMOLYTIC │ AUTOPSIES │STREPTOCOCCUS│STREPTOCOCCUS ─────────────────────────────┼─────────────┼─────────────┼───────────── Lobar pneumonia with red │ │ │ hepatization │ 16│ 6│ 37.5 Lobar pneumonia with red and │ │ │ gray hepatization │ 28│ 6│ 21.4 Lobar pneumonia with gray │ │ │ hepatization │ 20│ 1│ 5.0 ─────────────────────────────┴─────────────┴─────────────┴───────────── Notwithstanding the longer duration of the disease and consequent prolongation of exposure to infection, lobar pneumonia, which has reached the stage of gray hepatization, has shown the smallest incidence of infection with hemolytic streptococci. In the stage of gray hepatization there is diminished susceptibility to secondary infection with this microorganism. Characteristic histologic changes have been found in the lungs of those who have died with lobar pneumonia followed by invasion of lungs and blood by hemolytic streptococci (_e. g._, Autopsies 273, 430), but with no evidence of suppuration found at autopsy. Within the pneumonic lung occur patches of necrosis implicating both exuded cells and alveolar walls; in some places nuclei have disappeared; elsewhere nuclear fragments are abundant. In these patches of necrosis Gram-positive streptococci in short chains occur in immense number. In some instances (_e. g._, Autopsies 273, 346, 479) interlobular septa are very edematous and often contain a network of fibrin; lymphatics are dilated and contain polynuclear leucocytes in abundance. Streptococci are found within these lymphatics. The histologic changes which have been described represent the earliest stages of abscess formation and interstitial suppuration, lesions almost invariably caused by hemolytic streptococci. [Illustration: Chart 2.—Showing the relation of (_a_) date of onset of cases in which autopsy demonstrated lobar pneumonia, indicated by upper continuous line with single hatch, and of (_b_) date of death of these cases, indicated by lower continuous line with double hatch to (_c_) the occurrence of influenza, indicated by the broken line, and to (_d_) the total number of fatal cases of pneumonia, indicated by the broken dotted line. Each case of fatal pneumonia is indicated by one division of the scale as numbered on the left of the chart; cases of influenza are indicated by the numbers on the right of the chart. ]