The injection of parathyroid extract-Collip leads to decalcification of the skeleton. In regions of greatest decalcification secondary changes appear, with the result that fibrous bone lesions of the nature of ostitis fibrosa are produced.1 In animals suffering from acute and chronic hyperparathyroidism, the so-called characteristic lesions are severest and most easily produced in young animals. The bones or portions of bones most affected are the metaphyses of the long tubular bones and the portions of the cortex of the shaft nearest the epiphyseal cartilage plates, the costochondral junctions of the ribs, the cortex of the ribs used most in the respiratory act and the bones of the skull and the lower jaw.
It was decided to investigate the condition of the bony capsule of the labyrinth during acute and chronic hyperparathyroidism. The labyrinthine capsules of animals so affected showed on the whole almost complete absence of changes, although the