Reactions of the Dentinal Fibril to External Irritation**From the Research Laboratory of the School of Dentistry, University of Louisville.Work supported, in part, by a grant from the Research Commission of the American Dental Association.Read before the Section on Histology, Physiology, Pathology, Bacteriology and Chemistry (Research), at the Seventy-Second Annual Session of the American Dental Association, Denver, Colo., July 22, 1930.