Calcium concentrations in serum, cerebrospinal fluid (CSF), and perilymph were determined before and after the induction of a hypocalcemic state by a simultaneous injection of thyrocalcitonin and phosphate in the chinchilla. Prior to injection, the perilymph and CSF calcium concentrations were about equal and were approximately 70% of the serum calcium concentration. 1 h after the injection of thyrocalcitonin, serum calcium levels dropped by about one fourth and remained approximately stable for 3 h, whereas perilymph and CSF calcium concentrations showed no parallel decline. These results suggest the existence of mechanisms which are responsible for the maintenance of constant level of important cations in perilymph.

Rats were given low fluoride diets labelled with radiocalcium and either de-ionized water or de-ionized water containing 25 ppm fluoride. The percentage of calcium and specific activity (⁴⁵Ca/mg ⁴⁰Ca) of auditory ossicles were determined. An effect of fluoride on the calcium metabolism of normal auditory ossicles was demonstrated. The stapedes of animals receiving low fluoride water contained more calcium at 6 weeks than the stapedes of animals of both groups sacrificed at 9 weeks, and the comparative specific activties of ⁴⁵Ca suggest that the turnover of the calcium in ossicles from animals of high fluoride intake at 9 weeks of age is less than those of the low fluoride animals. The ratio of the specific activity of the stapes to the specific activity of the incus or malleus demonstrated that the stapes is a much more metabolically active bone than the other ossicles.