Figure 4. Light micrographs of the basal turn from a rat exposed to octave band noise at 13.6kHz (100 dB) under a duty cycle of 40% + carbon monoxide (1200 ppm) and from a rat exposed only to octave band noise (100 dB) under a duty cycle of 40%. Staining for succinate dehydrogenase showed a loss in isolated outer hair cells from the subject exposed to carbon monoxide alone but wide-spread loss in outer hair cells of the subject receiving both noise + carbon monoxide. Inner hair cells appear to be well stained in subjects from both groups.