Bone destruction may be molecular, to which the name of caries is applied, or en masse, when it is spoken of as necrosis. Caries is usually produced by the milder and slowly acting circumscribed affections in which bone destruction keeps pace with bone death. On the other hand, necrosis results from the more rapidly acting and severer processes in which a more or less extensive area becomes involved and destroyed in a comparatively short time and which persists for an indefinite period before removal. Before considering the special subject of necrotic bone and its subsequent changes it is well to glance briefly at the subject of tissue necrosis in general in order to determine the differences which obtain for bone, and the reasons for their occurrence.
The death of tissue en masse occurs either from infection or from circulatory disturbances which may be acute or chronic in nature. When due