In a previous report by one of us,1attention was called to the possible relation of otosclerosis to rickets or to the deficiency disease of which rickets is a common manifestation. The purpose of this second report is twofold: (1) to determine the pathologic changes within the temporal bone, particularly in parts most intimately associated with the function of hearing, in experimentally produced conditions having a fundamental resemblance to rickets, and (2) to establish an analogy between these changes and those found in that important and prevalent progressive type of deafness named "otosclerosis," thus attempting to offer experimental evidence as to its cause, i. e., that it is a manifestation of a deficiency disease. Until 1902, Moos and Steinbrügge, according to Politzer,2were the only two who had minutely investigated the changes in the labyrinth of rickets. Necropsy of a dumb idiot, deaf since birth, who had general