[Tubular structures revealed using tannic acid on the surface of the epithelium of the tympanic cavity of the chicken].

We have studied the ultrastructure of the epithelium lining the tympanic cavity of chicken, using two embedding techniques. In certain cases, the epithelium was minced in Karnovsky fixative, post-fixed in osmium, dehydrated and embedded in Epon, following the usual methods. No morphologically detectable structures were seen at the level of the epithelium surface. In other cases, the epithelium was immersed in Karnovsky fixative and subsequently in glutaraldehyde (1%) to which, however, tannic acid (1%) was added; the specimens were then osmicated, dehydrated with Epon and embedded in polar Epon mix. This method was sometimes used to study the alveolar surfactant, since this makes it possible to preserve its phospholipid fraction. The epithelium, in this way, is seen to be covered by an electron-dense material made up of thin, intertwined tubules. The hypothesis formulated is that the tubules are related to the presence of surfactant substances.