A series of fourteen rabbits were studied by roentgenograms made twice a month after injection of zinc beryllium silicate. After death or sacrifice, twelve long bones from ten rabbits were studied by microradiography and celloidin-embedded contiguous sections stained by hematoxylin and eosin. Spalteholz preparations of bones from four additional rabbits were also studied after injection of the arterial tree with a mixture of gelatin and India ink.

The following observations were made: Medullary formation of bone was detected from the roentgenograms made eight to sixteen weeks after the last injection in all fourteen rabbits. Microradiography disclosed that this bone had a higher mineral content than the surrounding normal bone. In certain areas in this medullary bone, the lacunar spaces were blurred or indistinct on microradiography. Contiguous histological sections revealed that similar areas in sections stained by hematoxylin and eosin were devoid of cells. Therefore, it is postulated that the blurred lacunae evident in the microradiograms represent areas where the cells have died and mineralization of the empty lacunar spaces has occurred. Part of this phenomenon may be due to the direct cytotoxic effect of the zinc beryllium silicate seen in marrow spaces adjacent to the apparently non-viable, acellular bone on the surface of viable trabecular bone. Also, this phenomenon may be due to a decrease in vascularity caused by blockage of the blood supply by the abnormal bone. The decrease in vascularity, however, could be due purely to the cytotoxic effect of beryllium.

Osteogenic sarcoma made its appearance thirty to fifty-two weeks after the last injection of beryllium. The morphological appearance of this phase is commented on, particularly the differences between the timorous bone and the abnormal medullary bone of beryllium poisoning and the similarity between this tumor and human osteogenic sarcoma.