(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. This condition commences in the involuntary muscles, and in the heart may simulate hypertrophy of that organ, then passes into the voluntary muscles of the back of the neck and lower jaw, and then into the muscles of the face, front of the neck, chest, and upper extremities, and then into the trunk muscles, and last of all, into those of the lower extremities. In most cases it passes off in the same order, the body becoming quite flaccid, the _rigor mortis_ never returning. These phenomena occur whilst the body is cooling. The muscle becoming rigid is dying, the rigid muscle is dead. The cause of the _rigor mortis_ is held to be due to the coagulation of the myosin. The reaction is acid from the presence of sarcolactic acid, but becomes alkaline during putrefaction. If fresh difibrinated blood be passed through the rigid muscle, it will become flaccid, and respond by contraction to electric stimulation.