If the hearing sensitivity is plotted graphically, the line joining the points of minimum audibility will seldom, if ever, be an even line, but will vary at certain frequencies up and down. This is the case in both normal and abnormal ears. By the use of tuning forks, cylinders, whistles and sirens, it was discovered that in certain abnormal ears, so-called "tone-gaps" occurred; in other words, that within certain narrow frequency ranges, no sound was heard by the ear being tested, although the frequencies to each side of these areas were easily heard. Audiometric measurements 1 prove that the true tone-gap is not a fact, because one never finds a true tone-gap. The reason no sound was formerly heard in these so-called tone-gaps was that the sounds used for testing were not loud enough. If the sounds had been loud enough, they would have been heard. Thousands of audiograms have