Instantaneous rigor following violent death has been assumed to be ordinary rigor mortis, hastened in development by circumstances, or a rigidity of tetanic character. Dr. Carpenter, the English physician, held to the latter theory, and believed that the rigidity ceased after a few hours, to be succeeded by relaxation and ordinary rigor mortis in turn. Dr. Brinton, reviewing all other theories, claimed that the phenomena on the battlefield are unique. "Ordinary rigor mortis," he wrote, "is developed after muscular irritability has ceased, but before putrefaction sets in. The appearance of battlefield rigor is probably synchronous with violent death.
"In ordinary rigor mortis the march is downward; the parts first affected are the neck and jaw; the lower jaw, if previously relaxed, is drawn up; flexor muscles are supposed to be affected in a greater degree. Battlefield rigor affects probably all regions alike at once.
"Ordinary rigor mortis is usually of twenty-four to thirty-six hours' duration; battlefield rigor remains longer than is supposed. . . . The prolonged continuance shows that it is not tetanic nor followed by rigor mortis proper." The doctor saw cases of it twenty-four to forty-eight hours and once sixty hours after death. Armand saw it at Magenta twenty-four hours old and Perir at Alma forty-eight hours after death. Dr. Brinton's paper closes with this brief summary of the distinctive features of battlefield rigor:
"The rigor is developed at the instant of death.
"The cadaveric attitudes are those of the last moment of life.
"The death most probably is instantaneous and unaccompanied by convulsions or agony.
"The rigor is probably more lasting than is usually supposed.
"It is extremely doubtful whether this instantaneous rigor of sudden death or rigor of the battlefield is succeeded by flexibility, in its turn to be followed by ordinary rigor mortis."
This subject lies, of course, beyond the realm of experiment. If rigor mortis is due, as is believed, to solidification of the juices of the muscles by the acid conditions developed therein, marked chemical changes, either rapid or prolonged, follow death under ordinary circumstances. In what degree may the solidification be hastened by extraordinary violence in death? We learn that protoplasm is subject to peculiar changes under peculiar conditions; that it contracts under electric shocks, and that certain forms of it coagulate under temperatures varying from 100° to 122° Fahr., a species of "heat-stiffening" illustrated by the coagulation of the white of an egg. The presence of certain salts will cause muscle juice (myosin) to coagulate at a temperature possible to be attained in the system of a hard-working man on a hot day.