(2) On what parts of the body usually seen?—On the most dependent parts of the body; on the whole of the back of the body, if the body be supine. The patches are irregular and slashed, terminate abruptly, and do not fade gradually into the surrounding colourless skin.
(3) At what period after death first observed?—In from eight to twelve hours, gradually extending in size till putrefaction sets in.
(4) Whether or not affected by death from hæmorrhage?—Formed after every kind of death, even after death due to hæmorrhage, although the coloration may not be quite so marked.
(5) Hypostasis is liable to be mistaken for ecchymosis—the result of injury.—Hypostasis must also not be confounded with the livid patches seen on the legs and feet of aged persons and on those who have died from typhus, chronic renal and cardiac disease, &c. The rose patches—“frost erythems”—seen on those who have died from exposure to cold, must not be mistaken for ecchymosis. The above patches are as frequently on the upper surfaces of the body as on the lower, and are not so extended as cadaveric lividities; the blood, moreover, which gives rise to them is diffused through the areolar tissue, and not incorporated with the true skin.
(6) How distinguished from ecchymosis?—Effused or coagulated blood is found when an incision is made in a true ecchymosis, however small, whereas a few bloody points are alone seen on a slight or deep incision into a post-mortem stain or true hypostasis. The seat of hypostasis is the superficial layer of the true skin. Hypostases are never raised above the surface, as ecchymoses sometimes are. In describing these two conditions, “ecchymosis” and “hypostasis,” it is preferable to describe the former as “discoloration from extravasated blood,” and the latter as “lividity after death.”
10. Cadaveric rigidity.—From the moment of death till the time when putrefaction sets in, the muscular structures of the body may be said to pass through three stages:—
(1) Muscular Irritability.—The muscles flaccid, but still possessing the power of contractility on the application of certain stimuli. Parts contracted during the act of dying—cadaveric spasm—as the muscles of the hand grasping a knife or other weapon, may continue so for some time after death.
(2) Cadaveric rigidity.—A state of rigidity, the power of contractility absent.
(3) Commencement of Putrefaction and Chemical Change.—Relaxation again present; all power of contraction lost, not to be regained.
Cadaveric rigidity, or rigor mortis, is a purely muscular phenomenon, and is not dependent on the nervous system, as it is not prevented, though it may be delayed, by division of the nerves, and is as well marked in paralysed as in non-paralysed limbs. Cadaveric rigidity, which occurs early in the heart, must not be mistaken for hypertrophy, or its absence for dilatation. In every case the rigor mortis precedes putrefaction, and consists in a shortening and thickening of certain muscles, chiefly the flexor and adductor muscles of the extremities, and also the elevators of the lower jaw.