These tumors may arise from the marrow, but generally in the epiphysis of the bone and extend to the shaft only at a later stage of their development. As the tumor advances, it causes a softening and an absorption of the original cellular marrow until it approaches the periosteum. In many cases the periosteum, as about any form of foreign body, then begins to proliferate and forms a shell of periosteal bone surrounding the tumor. In that way the shell of the bone oftentimes becomes very much enlarged before there is any extension of the process through the shell to the adjacent tissue. By destruction of the marrow and of the cortex, great softening of the bone may occur so that spontaneous fractures not infrequently are seen. Other sarcomata arise from the periosteum, and usually originate from one side of the bone, although occasionally they entirely surround the bone. In the periosteal sarcomata, a new formation of bone is common and the bone is frequently arranged in a radical way, giving a most remarkable picture on the X-ray plate. +Myeloma+ is a very rare malignant tumor of bone. Such tumors always appear only in connection with bone, are usually multiple, and are of the same type as other lymphoid tumors. The cells of such tumors resemble very closely the type of plasma cell. These cells are arranged in masses without an intercellular substance, and the tumors are closely allied to the malignant lymphomata. The cases are always associated with albuminuria. +Symptoms.+ The chief symptoms of malignant tumors are swelling and pain, both of which oftentimes are extreme. The swelling may be spherical or spindle shaped. +Extension+ to the joints may not occur for a great length of time. In many cases X-ray examination is the most reliable method of detecting the character of the bony change. +Treatment+ of all sarcomata is early and complete removal. This means in nearly all cases, amputation of the affected bone, and it is important that the amputation should be of the entire bone through the joint between the bone and the body, rather than amputation of the bone in continuity. The reason for this is, that even in sarcomata, which have not extended to the soft parts, very frequently there have occurred metastases of tumor-cells throughout the blood sinuses of the affected bone, often times at a distance of several inches from the site of the original primary tumor. +Carcinomata.+ Cancer of bone always is secondary to cancer in some epithelial organ. The infection may take place by direct extension through the blood or the lymphatics. In cases of metastatic invasions of bone, spontaneous fractures oftentimes are the first symptom which calls attention to the fact that metastases have occurred.