Khoor A, Gray ME, Hull WM, Whitsett JA, Stahlman MT. Developmental expression of SP-A and SP-A mRNA in the proximal and distal respiratory epithelium in the human fetus and newborn. J Histochem Cytochem. 1993 Sep;41(9):1311–9. doi: 10.1177/41.9.8354874. PMID: 8354874.