The pathology of the pulmonary lesions in acute epidemic influenza is so distinctive that except for the late purulent stage which may resemble types of reinfected and unresolved pneumonia the condition cannot be confused with the stages of frank lobar pneumonia. We appreciate that this is a very positive statement, and that opposition will be taken by those who resting their opinion upon individual factors may claim that a clear distinction from other forms of pneumonia is not available. We, however, base our opinion not upon a single feature, but upon the combined pathological complex observed in many individual cases. These features are mainly those seen in the type of the lesion, the character of the distribution, extent of involvement and the multiple stages so commonly present at one time in different portions of the lung. The type lesion that has become so well known in pneumococcus lobar pneumonia has its distinctive stages which for teaching purposes are divided into the stage of (1) congestion, (2) red hepatization, (3) gray hepatization and (4) resolution. In dealing with lobar pneumonia from the standpoint of illustrating these stages the majority of teachers annually confess their inability to present for the student’s study the stage of congestion. The student is impressed that the congestive stage of lobar pneumonia is very transient and rapidly passes into the stage of red hepatization. Patients do not die with pneumococcus pneumonia in the stage of congestion. And this is also largely true of the stage of red hepatization, which is but rarely seen at the autopsy table. This community (Pittsburgh) gives its large quota to the mortality statistics of pneumococcus pneumonia, but it is most unusual to meet with a specimen of red hepatization except for the borders of the advancing gray area. And, furthermore, red hepatization even when found in the unusual cases shows remarkably little of this character when seen under the microscope. True it is that a certain number of red blood cells will be found in the alveoli and a certain degree of congestion will occupy the alveolar walls, but its extent is far less than what we may have hoped to demonstrate to others. So that broadly speaking the intensely congested lung with or without red hepatization is unusual in our frank lobar pneumonia. This was quite the reverse in our cases of acute epidemic influenza-pneumonia. Furthermore lobar pneumonia in the great majority of instances illustrates a distribution distinctive for the name. Massive lobar, or pneumococcus pneumonia is found to occupy one or more lobes or parts of lobes. The involved lobe is fairly uniform in the stage of the inflammatory process. If it is in the early gray stage, this will be seen with equal intensity in the different areas of the lobe. Patches of pneumonia in different stages within the same lobe are not to be found, while this finding is not uncommon in the pneumonias of acute epidemic influenza.