Large, solitary air cysts or "balloon cysts" of the lung have been reported by few observers. In 1925, Koontz1 made an exhaustive review of the literature, and tabulated 108 cases of congenital cystic disease of the lung. The cysts in 7 of this number were large, solitary air sacs, the remainder being small and, usually, multiple.
In 1859, Hermann Meyer2 described a solitary large cyst, and remarked on the rarity of reports of similar cases in the literature at that time. The earliest report was made by Bartholinus.3
The following report is of interest because the patient was under observation the greater part of her life, and because thorough postmortem studies seem to throw light on the etiology of this disease.
REPORT OF CASE
History.—B. W., a white girl, aged 17½ months, was the first child of healthy young parents. The mother's pregnancy and labor had