NECROSIS. This word, which has the same meaning as mortification, is now restricted in surgical works to death of bone. It is sometimes used to signify the part which dies ; it may, however, with more propriety signify the process, ending in the death of the bone. A severe inflammation, caused by a severe blow, by cold, or by the absorption of various poisons, as mercury and phosphorus, is the general precursor of necrosis. The dead part, analogous to the slough in the soft tissues, is called a sequestrum or exfoliation. At first it is firmly attached to the living bone around ; gradually, however, the dead portion is separated from the living tissue. The process of separation is a slow one. New bone is formed around the sequestrum, which often renders its removal difficult. As a rule the surgeon waits until the dead part is loose, and then cuts down through the new case and removes the sequestrum. The cavity in which it lay gradually closes, and a useful limb is the result.