Hematoxylin and eosin staining of the middle ear in adult mice. (a, b) The middle ear of an unaffected animal. This has a clear middle ear cavity (MEC), external auditory canal (EAC) and a thin, single cell mucosal lining of the cavity. (c, d) An affected animal with a normal EAC, but effusion within the MEC and a thickened mucosa, with fibroblasts, granulocytes and granulation tissue. (e) A magnified view of the effusion in an affected animal, containing foamy macrophages and neutrophils. M, malleus. Scale bars: 100 μm (a, c); 20 μm (b, d, e).