Post-operative volume determinations have been made of the ear canals of 93 chronic ears operated on radically (removing the bony posterior meatal wall at operation, obliterating the surgical cavity by musculoperiosteal flap, and reconstucting the meatus, by soft-tissue only in 81 ears, or by cortical bone chips and soft tissue in 12 ears), and of 30 normal ears, using a liquied-filling method and by determining the compliance of the ear canal at a pressure of +200 mm. H2O.

The liquid-filling method gave more exact results than did the impedance measureemnts, and the results of the later showed more dispersion in all groups of ears. In 51 ears without post-operative cavities and reconstructed without bone chips, the mean value of the ear canal volume was 0.9 ml. by the liquid-filling method, and 1.5 ml, by the compliance method (p<0.001). The corresponding values for 30 ears with post-operative cavities, but without bony reconstruction of the meatus, were 1.5 ml. and 1.9 ml. (p<0.01). The values were 0.9 ml. and 1.2 ml. in 12 ears with posterior canal walls reconstructed with bone chips (p<0.01), and 0.8 ml. and 1.0 ml. in 39 normal ears (p<0.001). The liquid method seems to be a very exact method, but quite trouble-some in routine clinical use; the compliance method is suitable in most ears in which there has been bony reconstruction of the posterior meatal wall, but not in ears in which the posterior ear canal wasll has been reconstructed with solft tissues only, because the soft posterior meatal wall was mobile at +200 mm. H2O pressure.