D. THE HYALINE NECROSIS OF THE PULMONARY TISSUE
The hyalinization of the epithelium lining the ducti alveolares (47, 48) also merits special attention (Figs. [V], [XV], [XVI]). This process may extend through the wall of the duct and is often seen in the alveolar walls throughout the involved lung. The entire alveolar wall may be homogeneous in appearance, but, occasionally, the thrombus alone, which has formed in its vessels (41), presents this change (Fig. [XVII]). The alveolar as well as the bronchiolar wall is thickened by a homogeneous material in which cell-body and exudate cannot be differentiated. This acute necrosis, as has been mentioned, is encountered in gas poisoning but is unusual in other known types of respiratory infection. Doubtless, it is a precursor to the more destructive lesions commonly found in later stages of the disease—abscesses which extend through the bronchiolar walls (Fig. [XXXI]), necrotizing areas of pneumonia in which huge clumps of bacteria are found (Fig. [XXXII]), and true gangrene (Figs. [XXXIII], [XXXIV], [XXXV]). The destruction of the alveolar wall in the early stages of the disease plays a causal rôle in the production of subcutaneous emphysema (Figs. [XVIII] and [XIX]). This important phase of the histological change in influenzal pneumonia has received but little attention and, with one or two exceptions, is not mentioned in the literature (8, 162).
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.