The diverse and frequently extensive manipulations of the nasal mucous membranes involved in surgical procedure on the nose and paranasal sinuses have generally been initiated and governed by the final results obtained. Most of the literature on experimentation on animals also has been devoted to this end. Such information would be enhanced and the rationale of some methods would be better evaluated if the primary reactions of the tissues to injury and the sequence of changes under different conditions were known. It has been the purpose of this study to supply at least some of that information. It might be assumed by the pathologist and the clinician familiar with regenerative processes in other parts of the body that these data are already available, but a review of the literature on the nose and trachea reveals that information of this sort is lacking for the pseudostratified epithelium characteristic of these