In Fig. 2 there has been extensive shedding of the epithelium and broad sheets of fibrin are attached to the alveolar wall. On the right the exudate has escaped from both sides of the alveolar wall and the network of fibrin has begun to appear beneath the epithelium on its upper side. Owing, however, to the fact that the epithelium is still intact, though slightly raised from the surface, no pore has been formed.

In Fig. 3 the exudate has found its exit from a very definite point and has been converted into fibrin which radiates into the alveolus. No pore has resulted because the epithelium on the opposite side of the alveolus is still intact.

In Fig. 4 the epithelium has been pushed off from diametrically opposite sides of the alveolar wall and a pore has been formed with a thread of fibrin passing from one alveolus to an adjoining alveolus.

Pores are as numerous in edema due to mitral stenosis with in sufficiency of the valves as in pneumonia, but there are no threads of fibrin to direct attention to them.

This study confirms my previously expressed opinion-pores are not normal, preformed openings.