Functions of the alveolar lining.

In 1953, Julius Comroe gave his Harvey Lecture on the functions of the lung (I). Most of his lecture concerned observations on factors directly affecting pulmonary gas exchange; but at the end, he devoted several pages to what he termed, functions of the These he considered from histologic, chemical, and physiologic points of view. He mentioned the rich innervation of the lung and its potential for neural regulation. He indicated that a wide variety of cell types is found in the lung. He called attention to the abundance of certain substances, such as histamine, heparin, dearing factor, and deaminating enzymes, which were commonly associated with other organs, and he questioned their role in the lung. He listed physiologic reactions by which the lung may protect against environmental hazards, circulatory stresses, and systemically generated poisons and particles. In 1953, these ideas were largely speculative. Now, in 1976, most of them have been investigated, and we can see that Dr. Comroe's crystal ball (his Prospectroscope) was incredibly dear. Today, no one is surprised that as much as one fifth of this symposium on cardiorespiratory function deals with nonventilatory activities of the lung. One of these activities is the maintenance of a stable, air-filled parenchyma through regulation of the properties of the extracellular lining of the alveoli, and this is the subject of my paper. The alveolar lining is a relative newcomer to the list of architectural components of the lung parenchyma, and it has received compara-