The Histology of the Isolated Perfused Lung

A description is given of the histological changes found in the isolated perfused lungs of dogs. The perfusion was carried out with heparinised blood under negative pressure ventilation for 3½ to 7 hours. The main findings were: (1) Œdema: comprising alveolar exudate, distension of periarterial lymphatics and œdema of arterial walls. (2) Periarterial and peribronchial hæmorrhage. (3) Collections of polymorphonuclear leucocytes in the small pulmonary blood vessels. (4) Dilation of bronchi and bronchioles. (5) Vascular congestion of bronchial walls (except in experiments in which the outflow was allowed to drain from the open pulmonary veins). The alveolar walls, bronchial epithelium and vascular endothelium were normal and there was no pulmonary vascular congestion. It is pointed out that changes (1) and (2) have been recorded in other types of experimental lung damage and they seem to represent a common reaction of the lung to various modes of injury. The possible causes of these changes are discussed. The histological changes which have been described in the lung of the heart‐lung preparation were for the most part not found in the isolated perfused lung. The perfusion experiments which provided the material for this investigation were performed by Miss Catherine Hebb, and the author is indebted to her and to Professor de Burgh Daly for much helpful discussion.