Revaluation of numerous factors in the study of human immunity has made necessary the reconsideration of numerous data long accepted, among them a more accurate study of the minute structure of various tissues of the body. Difficulties in technic and in securing proper material have delayed such studies of sinus mucosa until very recent years. Not long ago, for example, Mosher, Knowlton and MacGregor demonstrated the regrowth of ciliated epithelium after radical removal of sinus membranes.
The whole problem of the cellular content of normal and of pathologic mucosal surfaces has seemed to us of fundamental importance, in the light of late discoveries elsewhere. I have, in other papers, elaborated the analogies and theoretical considerations that started us on the present series of preliminary experiments.1 It should here be stated that I have been unable to find any record of previous findings based on so-called "vital staining" of the