Editor—The letter from Hills and Masters1in response to my commentary of their paper2 raises some interesting points which require further comment.

I stand corrected over my description of their model of the alveolus as “dry.” This was a short hand term on my part to distinguish Hills’ theory on which he has published widely from the more traditional theories of how pulmonary surfactant works.

Their letter, however, does not challenge the basic points I made in reluctantly refuting their hypothesis. These were, firstly, that fetal lung liquid can be absorbed before birth—that is, before the establishment of an air–liquid interface and thus before surface forces can act—and secondly, that even in neonates …