HUMAN LUNG COLLAGEN 71 bation with muscle. In early experiments each individual slice was weighed and counts/mg wet weight/cc/minute determined. However, it became apparent that weight variation was insignificant, and this was discontinued.Results. Table I represents accumulated data from 5 experiments. Numerical values are the mean of 3 aliquots from each flask, and measured amount of radioactivity remaining after incubation. It is apparent that addition of PTE to the incubating medium consistently increased amount of radioactivity remaining and consequently must have inhibited uptake of CaA5 by muscle, or altered degree of absorption of Ca45 on the muscle cell membrane. Addition of PTE to the incubating medium in absence of muscle did not affect the final activity of Ca4s. The data were analyzed by Student-Fisher t test for significance of meam differences, and mean difference was significantly different from zero ( P value <.OOl).Sumnzayv and conclusions. Administration of parathyroid extract (PTE) elevates serum calcium ( 5). The present experiment indicates that PTE consistently inhibited in vitro uptake of calcium by rat voluntary muscle. This observation is compatible with the known hypercalcemic effect of parathyroid hormone and provides evidence for the hypothesis that parathyroid glands regulate movement of calcium between extracellular and intracellular fluid.Preliminary investigations indicate that collagen in human lung undergoes both quantitative and qualitative changes with increasing age( 1 ) . I t is already known that a quantitative change occurs in animals; collagen content of guinea pig lung(2) and of rat lung(3, 4) increases with age.

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