Abstract
Quantitative studies have, for the first time, been carried out on the single lung in a case of unilateral pulmonary aplasia, in which the other lung was represented by a rudimentary bronchial stump. The patient died at the age of 3 months. The lung was enlarged to almost twice the normal volume, filling the intrathoracic cavity. The bronchial generations were reduced in number. Pulmonary artery branches were also too few, the supernumerary being more reduced than the conventional; muscle had extended abnormally far into peripheral arteries. The alveolar number was twice the normal for one lung, that is, it represented the normal total for age; alveolar size was rather less than normal. The hypoplasia of airways and blood vessels represents an early intrauterine disturbance in lung growth, caused perhaps by the same factor that inhibited the development of the second lung; the increased alveolar multiplication probably reflects increase in available space during fetal life.