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v_                           MECHANICAL INJURIES

Fcs^medico-legal purposes mechanical injuries are divided into bruises
or contusiofes^ abrasions and wounds.


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

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.