A STUDY OF THE EFFECTS OF HYPERCALCÆMIA PRODUCED PARATHYROID HORMONE AND IRRADIATED ERGOSTEROL UPON THE ACTIVITY OF THE CEREBRAL CORTEX BY MEANS OF CONDITIONED REFLEXES

1. Hypercalcæmia produced in dogs by administration of parathyroid hormone or irradiated ergosterol caused functional disturbances in the activity of the higher nervous centres. 2. These disturbances are characterised by an exaggeration of the inhibitory process, shown by enhancement of the inhibitory after‐effect of negative stimuli, acceleration of the extinction of established conditioned reflexes, decrease and eventual disappearance of conditioned reflexes, and varying degrees of lethargy. 3. This exaggeration of inhibition may be temporarily dispelled by the administration of caffeine. 4. A temporary phase of excitation was noted at certain times during the administration of parathyroid hormone, but not during the administration of irradiated ergosterol. 5. The various types of treatment, which involved the maintenance of a marked hypercalcæmia over considerable periods of time, had little effect upon the health of the animals in general, or the sense of hearing in particular. The authors are deeply indebted to the Otoselerosis Committee of the American Otological Society for financial assistance. They wish to express their thanks to Professor B. P. Babkin, Professor J. B. Collip, and Dr D. L. Thomson for help and advice during the course of this work, and to Professor John Tait for his kindness in lending the oscillator used in the investigation. They also desire to acknowledge their indebtedness to Eli Lilly & Co. for the parathormone and to Mead, Johnson & Co. for the ergosterol used in the experiments.