1. A study has been made of the repair of bony defects in the calvaria of albino rats.

2. An accelerated rate of bone repair was observed in experimental defects into which chondroitin sulphate-treated demineralised bone was implanted.

3. Acid-soluble collagen reconstituted with chondroitin sulphate was also more effective as an implant than was acid-soluble collagen reconstituted with sodium chloride.

4. It is concluded from these studies that chondroitin sulphate treatment accelerated the rate of new bone formation induced by demineralised bone, by reconstituted acid-soluble collagen, and to a lesser extent by Gelfoam. It was also found that demineralised bone and fresh homogenous bone promoted bone repair, but that chondroitin sulphate-treated demineralised bone promoted the most rapid rate of bone repair among the substances tested.

5. The possible role of chondroitin sulphate in bone formation is discussed.

The alkaline phosphatase activity of pre-osseous tibial cartilage of rachitic bone stored in the deep freeze for two weeks at -25 degrees centigrade was only slightly less than that of fresh controls from the same animals. The deep frozen pre-osseous tissue did not calcify in in vitro calcifying media containing either inorganic phosphorus or organic phosphate ester. The fresh controls calcified equally well in both media. In addition, after deep-freeze storage the tissue hydrolysed the organic phosphate to the same degree as did the fresh tissue.

Bones heated at 65 degrees centigrade will calcify in vitro after calcium chloride treatment despite the destruction of phosphatase activity.

It appears unlikely that a relationship exists between alkaline phosphatase and the minimal system required for calcification of pre-osseous cartilage in vitro. These findings do not exclude the possibility that alkaline phosphatase plays some critical role in vivo.

1. The influence of various methods of preserving bone on the calcifying mechanism of the tibial epiphysial cartilage of rachitic rats was studied. An in vitro calcification technique was employed.

2. Preservation by deep freezing, aqueous merthiolate, boiling, or acetone inactivated the calcifying mechanism.

3. The inactivation was reversed with calcium ions, most readily in the deep-frozen bones, less readily in the merthiolate treated bones, still less readily in the acetone stored bones, and least in boiled bones.

4. Exposure to calcium ions before preservation in the deep-freeze chest prevented inactivation.

5. The inactivation, reactivation and survival of the calcifying mechanism were confirmed by metachromasia studies.

6. The theory of the mode of action of calcium chloride on reactivation and survival of the calcifying mechanism is presented.