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The electron microscopic alterations of the alveolar septum in advanced hemodynamin and alloxan-induced pulmonary edema were compared. Pulmonary edema was produced in anesthetized dogs by means of increased lefy atrial pressure and hemodilution and by allocan administration. Sections of pulmonary tissue from these dogs and similarly anesthetized controls were processed for and examined by light and electron microscopy. In the hemodynamic form of edema the interstitial fluid collects only in the collagen-containing portions of the septum. The endothelium, epithelium, their respective basement membranes and large portions of the air-blood barrier are unaffected. Alloxaninduced edema, in contrast, is characterized by degeneration of both endothelium and epithelium and by the appearance of fibrin within the alveoli. The hemodynamic type of pulmonary edema appears to result from an accentuation of the normal process of fluid exchange within the lung. Allocan-induced edema, on the other hand, is a pathologic process. The functional implications of these results are discussed.

Ideal points" would be found in only one tissue section each. Particles of finite size will be cut once or more depending on both their dimensions and the thickness of the sections. This represents a source of error in counting particles in tissue sections, which can be corrected with the above formula.

No abstract