Pores of Kohn.

The history of the investigations into interalveolar communications (pores of Kohn) shows that the question whether they exist and, if so, their nature has for approximately a century been contentious. The present electron microscopic study of the lungs of mice demonstrates that alveolar pores are normal structures, with edges composed of intact alveolar wall. A number of planes are demonstrated from w-hich a fully compatible reconstruction is made. It is concluded that pores are round or oval structures frequently having at least one type IL alveolar cell forming part of their boundary. It is further postulated that pores may be divided by a capillary column stretching across the space, resulting in two openings. A type H1 alveolar cell forming part of the pore wall may straddle the capillary column. Alveolar macrophages may be found lying free in the pore or lying astride a capillary column. When lying in a corner position type II cells may occupy the full wall thickness and face into three alveoli.