In the interpretation of this necrotization, the only helpful analogy is offered by the acute respiratory lesions following the inhalation of poisonous gases. With the aid of vital stains, it has been demonstrated that chlorine quickly initiates necrosis due to the direct action of the gas. Since necrosis also occurs with phosgene,—in the decomposition of which hydrochloric acid is probably liberated,—there is presumptive evidence that the halogen is responsible for the process. Studies are now in progress to determine the relation of the acid-producing properties of the different strains of organisms to the type and fate of the pneumonic exudate. E. THE ORGANIZATION PROCESS The similarity between the acute lesions of influenzal pneumonia and those following the inhalation of poisonous gases led to the prediction, in the early studies, that if the process were not terminated by death, the bronchiolar and alveolar changes would not result in a restoration of the tissue to normal, but in an organization which would in its turn bring about mechanical changes in the pulmonary tissue. This prediction has been fulfilled; obliterating bronchiolitis (Figs. XI and XLVIII), bronchiectasis (Figs. L and XII), and organizing pneumonia (47, 92, 156, 162) (Figs. XXXIX, XL, XLI, XLIV, XLV) have been encountered despite the fact that the time interval for fatalities from extraneous or subsidiary causes has been short. [Illustration: FIG. XLIV. THE ALVEOLAR WALLS ARE IN PART OBLITERATED. THE ALVEOLAR EXUDATE IS ORGANIZED BUT THE FIBROUS TISSUE STRANDS ARE SPREAD APART BY EDEMA. ] [Illustration: FIG. XLV. AUTOPSY NO. 163. ORGANIZATION OF THE ALVEOLAR EXUDATE AFTER THE SUBSIDENCE OF THE ACUTE PROCESS. COMPARE FIGURE XLIV. ] Resolution of the exudate in pneumonia, with the restoration of the tissue to normal, is a result at such variance with the usual fate of an inflammatory exudate, that it has attracted a great deal of attention. Perhaps the most striking results of the study of this subject have been published recently by Kline (69). Arguing from previous experiments (70) in which it was demonstrated that the circulation of the pneumonic lung is impaired, and that for this reason sufficient serum cannot reach the exudate to inhibit the proteolytic action of leucocytic ferments, Kline introduced normal serum into the consolidated lung by the tracheal route, and showed conclusively that this resulted in an organization of the alveolar exudate. This, of course, might explain resolution, but it is difficult to see without further study how serum can reach the exudate to inhibit autolysis, and in this way stimulate organization, in one case of pneumonia and not in another.