Etiology of Enamel Hypoplasia in Rickets as Determined by Studies on Rats and Swine**Research supported by grants from the American Dental Association and from the dental staff of the Johns Hopkins Hospital.From the Department of Chemical Hygiene, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, Md.Read before the Section on Biologic Sciences and Research at the Midwinter Clinic of the Chicago Dental Society, Feb. 4, 1931