GUM (Gumma), in medicine, is a tumour arising out of the substance of a bone; it is so soft as to yield to the finger. When these tumours are harder they are called tubers; when harder still, they receive the name of nodes; but the hardest tumours in bones are exostoses. In venereal patients such tumours often happen on the head, and even in the middle of the most solid bones. They seem to be produced when the vessels running between the bony laminae, being either obstructed or inflamed, are dilated, and so raise the incumbent laminae. Perhaps the bone degenerates too into a morbid softness. A softness of the bones sometimes succeeds abscesses of the adjacent parts; and sometimes the origin of the disorder is lodged in the substance of the bone, especially in the lues venerea; gummata have, however, been discovered, when no such adequate cause could be observed.