We cannot, however, correlate our findings with the classification of pneumonias as given by MacCallum. His claim for specific types of pneumonia as a sequel to influenza is based upon his statement that “no satisfactory evidence has been brought forward to show that the epidemic influenza is a bacterial infection. It is evidently a general or systematic infection not especially affecting the respiratory tract and analogous in many respects, as Bloomfield has pointed out, to the acute exanthematic diseases.” Thus we are confronted by two schools concerning the nature of influenza. The one claiming that epidemic influenza is essentially a disease of the respiratory system and the other completely denying this. I am unable to understand the claims which are put forward to substantiate the second view. The classification of the pneumonias as suggested by MacCallum would be valuable if it could be applied in a practical manner. We find, however, that his description for the pneumococcus-pneumonia hardly coincides with common observations on endemic pneumonia and if the description is to apply only to the pneumonias associated with influenza wherein pneumococcus alone is isolated we find that our own observations do not coincide with this. The picture offered by MacCallum under this heading was reproduced when the bacteriological findings illustrated the presence of organisms other than the pneumococcus or combinations of these. The most characteristic of his description is the one for the streptococcus-pneumonia which when present alone gives quite a unique picture. The picture, however, is to a certain degree modified by the reactions which precede the streptococcus in the lung. Furthermore to offer as a characteristic picture for the influenza infection of the bronchi the presence of a thick yellow pus is hardly complete inasmuch as this exudate appeared only as a stage in the inflammatory process. The intense serous and hemorrhagic response observed early in this type of infection is more unique than the presence of pus which appears somewhat later and which may occur with infections other than the B. influenzæ. It has long been the hope in pathology to be able to establish by the character of the tissue reaction, the nature of the infecting agent. Up to the present this has been possible only with a very few types of bacteria. _Lung—Stage of Resolution_