Abstract
1 . Normal and diseased bone was obtained by biopsy from five patients suffering from Paget's disease. The tissue was studied by histology, microradiography and quantitative fluorescence microscopy using tetracycline markers. Study of the morphological changes showed that two of the biopsies could be regarded as normal, while one was osteoporotic; two biopsy specimens were in the porotic phase of Paget's disease and the remaining five were in the sclerotic phase.
2. The tetracycline markers were used to measure the linear rate at which bone was deposited on individual surfaces (appositional growth rate) in µ per day and the percentage volume of new bone added to the total volume of bone per day (bone formation rate). The values obtained for appositional growth rate in all the biopsies were of the order of 1 µ per day, but slightly higher values were obtained in the diseased tissue of each individual. The bone formation rate in normal bone from the proximal femur was about 0·04 per cent per day, about 0·13 per cent per day in the porotic phase, and about 0·4 per cent per day in the sclerotic phase of Paget's disease.
3. Although these values must be accepted with some reservation, there seems to be no doubt that there is an upper limit of about 1 µ per day to the rate of deposition of bone on an individual bone surface; this suggests that in Paget's disease the osteoblast behaves as a normal cell.
