It is to be borne in mind also, and especially from the medico-legal point of view, that, as early callus does not cast a deep shadow in a radiogram, the appearance of fracture may persist after union has taken place. The earliest shadow of callus appears in from fourteen to twenty-one days, and can hardly be relied upon till the fourth or sixth week. The disturbed perspective produced by divergence of the rays may cause the fragments of a fracture to appear displaced, although in reality they are in good position. If the limb and the plate are not parallel, the bones may appear to be distorted, and errors in diagnosis may in this way arise. In this relation it should be mentioned that perfect apposition of the fragments and anatomically accurate restoration of the outline of the bones are not always essential to a good functional result. * * * * * As most of the remaining signs are common to all the lesions from which fractures have to be distinguished, their diagnostic value must be carefully weighed. _Interference with Function._--As a rule, a broken bone is incapable of performing its normal function as a lever or weight-bearer; but when a fracture is incomplete, when the fragments are impacted, or when only one of two parallel bones is broken, this does not necessarily follow. It is no uncommon experience to find a patient walk into hospital with an impacted fracture of the neck of the femur or a fracture of the fibula; or to be able to pronate and supinate the forearm with a greenstick fracture of the radius or a fracture of the ulna. _Pain._--Three forms of pain may be present in fractures: pain independent of movement or pressure; pain induced by movement of the limb; and pain elicited on pressure or "tenderness." In injuries by direct violence, pain independent of movement and pressure is never diagnostic of fracture, as it may be due to bruising of soft tissues. In injuries resulting from indirect violence, however, pain localised to a spot at some distance from the point of impact is strongly suggestive of fracture--as, for example, when a patient complains of pain over the clavicle after a fall on the hand, or over the upper end of the fibula after a twist of the ankle. Pain elicited by attempts to move the damaged part, or by applying pressure over the seat of injury, is more significant of fracture. Pain elicited at a particular point on pressing the bone at a distance, "pain on distal pressure,"--for example, pain at the lower end of the fibula on pressing near its neck, or at the angle of a rib on pressing near the sternum,--is a valuable diagnostic sign of fracture. When nerve-trunks are implicated in the vicinity of a fracture, pain is often referred along the course of their distribution. _Localised swelling_ comes on rapidly, and is due to displacement of the fragments and to hæmorrhage from the torn vessels of the marrow and periosteum.