It is impossible to discuss within the allotted time all phases of the subject assigned to me, and the following facts about the diagnosis of middle and inner ear deafness are presented because I know they are accurate and think they will be of value in the interpretation of hearing tests. There are three common types of impairment of hearing: the type due to a lesion of the conduction apparatus which interferes with the transmission of sound to the cochlea; that due to a lesion in Corti's organ or the cochlear nerve which interferes with the perception of sound, and a combined conduction and perception deafness. It is possible to have impaired hearing due to a nuclear or auditory pathway lesion, but this is rare and when it occurs the patient always has symptoms of intracranial tumor or of a degenerative process in the central nervous system. Probably more than