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The history of the interpretation of osteitis fibrosa cystica generalisata as it was described in 1891 by von Recklinghausen (1) explains why the skeletal abnormalities were for so long considered to be the focal point of the clinical concept "hyperparathyroidism." During the 1930's, however , it was observed that many patients with hy-perparathyroidism showed no bone abnormalities on either histological or roentgenological examination (2). Recent publications show that only in one-third of the patients with hyperparathyroidism can skeletal deviations be demonstrated roentgeno-logically (3). This is remarkable, since a direct effect of parathormone on the skeleton has been established. It was demonstrated by treating nephrectomized rats with parathyroid extract (4), and by implanting parathyroid tissue under the skull of the mouse (5). Finally, it was shown that a cell-free parathyroid extract has a direct effect on tissue cultures of the parietal bone of mouse embryos and this by a reinforcement of the osteo-clastic bone resorption (6). The discrepancy between the clinical data and the pathophysiology of hyperparathyroidism might be explained by the assumption that the accelerated bone destruction caused by the hormone of the parathyroid gland is compensated for by an increase in bone production. If this hypothesis is correct, on the average, the bone of patients with hyperparathyroidism would be younger than bone of normal individuals of the same age. Evidence which supports this assumption has been found in animal experiments by using qualitative micro-radiography (7). Using autoradiography, Engfeldt and Hjert-quist (8) showed in 1954 that radioactive labeled phosphate is taken up in bone from a surrounding fluid, especially in young structures, and such * uptake occurs in the same regions in vivo as in dead bone in vitro. This observation suggests that the uptake of phosphate from a solution by dead bone in vitro could be used as a measure of the ratio between the amounts of young bone and old bone present in the sample. By young bone is meant newly-formed bone; by old bone is meant older osteons and fragments of older bone. Since the uptake of phosphate from a solution by dead bone under certain conditions is primarily an exchange reaction, labeling of the phosphate of the incubation medium is necessary to follow the uptake and release of phosphate from the bone. A method (9) for a phosphate "exchange" experiment in vitro was modified for the purpose of the present study, in such a way as …

STUDIES OF BONE OF PATIENTS WITH HYPERPARATHYDROIDISM BY MEANS OF PHOSPHATE EXCHANGE EXPERIMENTS IN VITRO AND QUANTITATIVE MICRORADIOGRAPHY*