FINE-STRUCTURE OF THE MIDDLE-EAR EPITHELIUM IN THE CHICKEN (GALLUS-GALLUS)

The epithelium lining the tympanic cavity of the chicken possesses dis tinct morphological characteristics. Its ultrastructure was studied us ing 2 preparative techniques. (1) After fixation in Karnovsky's soluti on, postfixation in osmium tetroxide and embedding in Epon, the epithe lium was observed to contain 2 kinds of cell: secretory and basal. The secretory cells (which we refer to as mixed granulated cells) showed numerous secretory vesicles that varied in appearance, some containing paracrystalline formations. The basal cells, located close to the bas ement membrane, showed no evidence of secretory activity. (2) Other sp ecimens were immersed in Karnovsky fixative and subsequently in a mixt ure of glutaraldehyde and tannic acid. They were then osmicated and em bedded in polar Epon mix. With this method, the epithelium was seen to be covered by electron-dense material made up of thin intertwined tub ules. In addition, the secretory cells contained vesicles with concent rically arranged lamellae; such vesicles resembled the multilamellar b odies of mammalian type II pneumocytes. The hypothesis is advanced tha t tubules and lamellar vesicles are related to the presence of surfact ant substances.