Studies of histological sections of implants in the anterior chamber of the eye in thirty-five guinea pigs and eighteen rats, made six weeks after implantation, revealed the following:

1. Injection of synthetic basic calcium phosphate apatite crystals resembling the inorganic crystals from natural bone resulted in a foreign-body reaction in four out of six guinea pigs.

2. Grafts of the femora of eighlteen-day rat embryos frozen at —18 degrees centigrade for twenty-four hours and then transplanted to the anterior chamber of the eye of adult rats survived in seven out of seven cases. Endochondral ossification was re-established. Similar grafts lyophilized under a vacuum of 0.1 millimeter of mercury for twenty-four hours also survived in six out of six instances. Embryonic femora transplanted directly without intervening treatment not only survived in five out of five animals, with reestablishment of endochondral ossification, but growth was much more active than in either of the two preceding groups.

3. Autogenous implants of fracture callus frozen at —18 degrees centigrade for twenty-four hours and implanted one week after fracture, survived in the anterior chamber of the eye for six weeks in one out of five guinea pigs. Fracture callus treated by lyophilizing for twenty-four hours prior to implantation failed to survive in six out of six cases. Fracture callus and spicules of adult bone transplanted without intervening treatment survived in four out of four instances.

4. Autogenous grafts of adult cancellous and cortical bone treated by freezing in five guinea pigs and by lyophilizing in six animals failed to survive in all instances. However. grafts transplanted directly survived in three out of three guinea pigs.

These studies, therefore, confirm the fact that homogenous grafts of embryonic bone and autogenous grafts of fracture callus and adult cancellous and cortical bone can survive and proliferate in a suitable ectopic site. Furthermore, embryonic bone frozen at —18 degrees centigrade or lyophilized under a vacuum of 0.1 millimeter of mercury for twenty-four hours will survive and grow when implanted in an ectopic location. Fracture callus and adult cancellous and cortical bone are less able to survive in an ectopic site following freezing or lyophilizing.