Editorial

The problem of lung growth Postnatal growth of the lung has excited controversy over many years. Much of the work on this subject has been conducted on small animals'-4 and it is not certain that results so obtained can be extrapolated to the human situation. Most attention has been centred on alveolar development. There are two possible modes of growth. Firstly, the animal could be born with its full complement of units (that is, alveoli), further increase in lung size occurring purely by increase in the volume of existing units. Secondly, there could be formation of new units. In rats there is rapid cell multiplication in early postnatal life, as shown by the sharp increase in the DNA content of the lung.57 Histologica