The mechanical stability of newly forming septa during postnatal morphologic transformation from saccular to alveolar lung : D.G. Talberta, D.G. Faganb, D.P. Southallc, aRoyal Postgraduate Medical School Institute of Obstetrics and Gynaecology, Queen Charlottes and Chelsea Hospital, Goldhawk Road, London W6 0XG, bDepartment of Histopathology, Queens Medical Centre, University Hospital, Nottingham NG7 2HU and Academic Department of Paediatrics, University of Keele, North Staffordshire Hospital Centre, Stoke-on-Trent ST4 6QG, UK