Determination of cocarboxylase in blood

RENEWAL OF INORGANIC PHOSPHATE IN BONE 601reaction in cancellous as compared with cortical bones, where the reaction is restricted to a few surface layers, but it does not explain the differ- ence in the rate of renewal between the cancellous bones of the rabbit and cat.There must be other factors, apart from structural ones, on which the rate of mineral salt turnover depends.Bone-salt renewal occurs in mature shaft bones mainly on the marrow side, i.e. in the same area where resorption is known to take place.Whether the two processes are connected with each other, e.g. through strain and stress, cannot be decided from the present experiments.But the close vicinity of such opposite processes rather suggests a cellular regulation (Newton, 1939).SUMMARY 1.The rate of tracer uptake in long bones varies according to species; the incorporation of 32P is considerably slower in the cat than in the rabbit or rat.2. No decrease of tracer concentration occurs in the cortical parts of the long bones of the rabbit, cat or rat, or in the cancellous parts of the two former species in the course of 30 days.The decrease of the specific activity of phosphorus in the cancellous bones of the rat is explained by the continued skeletal growth of this animal in adult age.3. The species differences are much better demonstrated with a newly developed technique, which affords an almost complete separation of the newly labelled bone salts from old-established bone.Large differences were found in the function of various parts of the shaft.4. The different aspects of bone renewal in the adult animal, such as initial uptake, recrystallization, Haversian replacement, mobilization of fixed iso- topes, equilibrium between bone and blood minerals, are discussed in the light of the new observations.I take great pleasure in thanking Dr H. J. Rogers for his continued interest in this work and for many helpful suggestions.