This paper reviews the results of several studies on the effects of blast wave exposure on the auditory system of the chinchilla, the pig, and the sheep. The chinchillas were exposed at peak sound pressure levels of approximately 160 dB under well-controlled laboratory conditions. A modified shock tube was used to generate the blast waves. The pigs and sheep were exposed under field conditions in an instrumented hard-walled enclosure. Blast trauma was induced by the impact of a single explosive projectile. The peak sound pressure levels varied between 178 and 209 dB. All animals were killed immediately following exposure, and their temporal bones were removed for fixation and histologic analysis using light microscopy and scanning electron microscopy. Middle ears were examined visually for damage to the conductive system. There were well-defined differences in susceptibility to acoustic trauma among species. However, common findings in each species were the acute mechanical fracture and separation of the organ of Corti from the basilar membrane, and tympanic membrane and ossicular failure.

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The amount and distribution of the post-natal bone deposition in the auditory ossicles and in the left tibia of dogs of varying ages were studied by means of alizarin labelling. The relative amount of fluorescent new-formed bone was expressed as a percentage ratio NB/(NB+PB) of new bone (NB) on the pre-existing bone (PB). The result was that the post-natal bone deposition (1) was larger in the tibia than in the incus, malleus and stapes; (2) significantly decreased with age both in the ossicles and in the tibia; (3) in the stapes it stopped at 3 months, while it was present in the tibia, incus and malleus even at 12 months. In the ossicles the post-natal bone deposition takes place both on the periosteal surfaces of the ossicles and on the internal surfaces of the haversian systems. The first process produces an appositional growth that stops in all three ossicles within the 1st month of post-natal life, the second one produces an internal growth that continues until the age of three months in the stapes, while in the incus and malleus it occurs in small amounts, even in the 12th month of life. In the ossicles all the new-formed bone tissue, periosteal and osteonic, is built up by primary bone (addition bone). In the tibia from 50 days of age the primary bone is gradually replaced by secondary haversian systems as a consequence of remodelling processes.

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