In this study, fractures were produced in animals which were being fed a diet that deranged their calcium and phosphorus metabolism.

At the end of three weeks, roentgenograms gave the impression that no union had occurred, but histological examination showed the presence of an excellent callus of bony tissue, although it was uncalcified.

Similarly treated animals, allowed to live four days longer and given vitamin D during this period, showed a rapid calcification of the bony callus which was, of course, already in existence. This rapid calcification of callus was noted in the roentgenograms. The histological appearance of the fractures changed little in this time.

Non-calcification of a callus is not non-union, because bony union is judged as such by the character and arrangement of the organic constituents of callus and not by its mineral content.

Vitamin D and other so-called calcifying agents do not control the formation or growth of a callus, and only indirectly affect its calcification.

As this experiment clearly separates the two phases of bone repair and illustrates that x-ray appearances of healing can be prevented by a failure of calcification even though a good organic callus is present, it is futile to adopt therapeutic measures directed at one process when the other is at fault, because the two processes are controlled by entirely different factors.

The possibility that certain cases of apparent meager or tardy union or even non-union in human beings are in reality cases of non-calcification should be considered.