CHAPTER X v_ MECHANICAL INJURIES Fcs^medico-legal purposes mechanical injuries are divided into bruises or contusiofes^ abrasions and wounds. BRUISES OR CONTUSIONS JBj-aises or contusions are injuries which are caused by a blow from a blunt weapon, such as a club (lathi), iron bar, stone, ball, fist, etc., or by a fall, or by crushing or compression. These are accompanied by a painful swelling and crushing or tearing of the subcutaneous tissues without solution of continuity of the skin. The swelling is due to the rupture of the subcutaneous blood vessels producing in the cellular tissues extravasation of blood, which is known as ecchymosis or effusion of blood. Ecchymosis makes its appearance over the seat of injury in one or two hours after the injury. It may appear even in less time, if the skin injured is very thin, as in the eyelids and scrotum. When ecchymosis has occurred into the deeper tissues or under tense fasciae, it appears on the surface at an interval of one or two days or even more at some distance from the seat of injury following the line of least resistance and in obedience to the law of gravity, e.g. the appearance of a black eye in the case of a contusion on the forehead or on the head. Sometimes, ecchymosis may not appear until after death, when a contusion has been caused within a few hours or a day or two before death. According to Sir Bernard H. Spilsbury1 this is not due to any appreciable addition to the blood in the contused area after death, but to a more rapid haemolysis of the stagnant blood as a part of post- mortem changes ; there is no circulation to carry away the pigment and the tissues are dead and cannot deal with it. The pigment diffuses locally, pro- ducing a stain in the surface, dark red at first, but changing sometimes to a bright red colour from absorption of oxygen through the skin; or an area of a dark green putrefactive discoloration appears over a deep bruise before the skin around it is changed. 3?he extent of ecchymosis depends, in ordinary circumstances, upon the nature"*and severity of the force used, the vascularity of the part struck, looseness of the underlying cellular tissues and the condition of the assaulted victim. Thus, ecchymosis will be extensive in lax and vascular tissues, such as the eyelids, scrotum and vulva and very little in tough and less vascular tissues, such as the scalp, palm of the hand or sole of the foot. Again, Jit may not appear in the abdomen even if a cart-wheel were to pass over the* body and cause death from the rupture of an internal organ. Ja cases of fatal internal injuries there may not be any sign of ecchymosis on the body, when a person is assaulted even with an iron-tipped lathi (blunt weapon), after he is covered with a thick rug, blanket or a quilt. No evidence of ecchymosis is also present if the weapon used is a yielding one, such as a sand-bag. J^chymosis is easily produced in children, flabby women and old people even by slight violence; on the other hand, it will be very slight if a person happens to be strong and muscular. ^i^certain pathological conditions, such as scurvy, purpura, erythema nodosura, haemophilia, malignant cases of infectious diseases, rashes due to the continuous use of drugs, and in the aged with sluggish circulation^ a slight blow or pressure may produce an extensive ecchymosis- ft* eases subcutaneous haemorrhages may occur spontaneously aii<! 1 Lancet, Feb. 28, 1925, p. 421.