Text-book of forensic medicine and toxicology

by R. J. M. Buchanan

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.

Cadaveric rigidity generally supervenes from eight to twenty hours after death, and may continue from a few hours to four or nine days.

The sooner rigidity comes on after death the sooner will it pass away, and the later the onset the longer it will last. It is a general rule that whatever exhausts the muscular irritability before death causes the early appearance and the more rapid disappearance of rigor mortis.

Conditions which modify the onset and duration of rigor mortis:—

(1) Age.—Transitory rigor mortis may appear in the immature fœtus according to the state of its muscular development.

It is feeble and disappears quickly in infants and young children.

It is usually well marked in adolescents and healthy adults, but feeble in old people.

(2) The Degree of Muscular Development of the Body.—Other things being equal, the greater the muscular development and muscular strength at the time of death, the slower is the onset of rigor mortis, and the longer its duration; the more feeble or exhausted the muscular condition, the more rapid the onset and the shorter its duration.

(3) The Temperature of the Environment of the Body.—In temperate and colder climates rigor mortis follows the usual course. A low temperature, below freezing-point, will retard the onset and favour the duration of rigor mortis, but if the body be suddenly thawed before rigor mortis has set in, it will appear rapidly and disappear more quickly than if it had not been subjected to the process of thawing.