METHODS

Animals are decapitated and temporal bones are removed and fixed in 2% phosphatebuffered glutaraldehyde within 10 min of death. For fixation, oval and round windows are opened and the fixative is gently perfused through scala tympani and scala vestibuli with a small pipette. Cochleas are left in glutaraldehyde for two hours, then rinsed overnight in buffer. After a second one hour buffer rinse, specimens are post-fixed for If hours in 1% OsO,. The osmium stains the membranous cochlea so that it can be identified through the bony cochlear capsule, facilitating bone removal and dissection. After fixation, temporal bones are rinsed in saline and dehydrated into 70% alcohol for dissection. Our acoustic trauma studies deal with lesions resulting from exposure to a 1 kHz pure tone. When lesions from the stimulus occur they are centered approximately 9 mm from the basal end of the cochlea (Hunter-Duvar and Bredberg, 1974). The lower middle and upper basal turns are therefore of greatest interest to us and our efforts are directed at the best possible preservation of structure in that area.

Dissection consists of thinning the bony cochlear capsule with a diamond dental burr until the osmium darkened spiral ligament is clearly visible through the bone (Engstrom et al., 1966). Beginning at the apex the bone is removed from around the membranous cochlea until the lesion area is reached. Care