1. In vitamin A deficiency, the replacement stratified keratinizing epithelium is morphologically identical in all locations.
2. All cells of the lowermost layer of the replacement epithelium have proliferative power as in the stratum germinativum of epidermis.
3. In recovery, in spite of the complete morphological masking, the epithelium in each region returns to its normal type.
4. The important histological features of repair involve removal of the layers of cells irreversibly differentiated towards keratinization and direct differentiation of the stratum germinativum into the normal type. These take place simultaneously.
5. The histological sequences observed in the removal of cells above the stratum germinativum indicate that autolysis as shown by vacuolar degeneration and heterolysis as shown by leucocytic infiltration are involved.
6. The cycle of A deficiency metaplasia and recovery affords an experimental method available for the correlation of nuclear chromatin and types of cytoplasmic activities.
