Micrographs of horse trachea fixed by immersion in non-polar fixative (A, B). Note that the lung lining layer (aqueous phase [asterix] and surfactant film at the air liquid interface [arrow]), has been preserved with this fixation technique. EP = epithelium, CI = cilia. Bars: (A) = 2 μm, (B) = 0.2 μm. Reprinted with permission from .