If a body already in a condition of early rigidity be exposed to a temperature of 75° C., the rigidity becomes more marked, since albuminates in the muscles, other than the myosin, become coagulated in addition. This phenomenon has been called heat stiffening.
(4) Mode of Death.—After all exhausting diseases of long or short duration, rigor mortis appears early and passes off quickly, as in death from phthisis, cholera, typhus fever, typhoid, hydrophobia, scurvy, and occasionally in chronic Bright‘s disease.
Death during alcoholic intoxication favours the duration of rigor mortis. After violent muscular exercise death is quickly followed by rigidity. Animals that have been hunted for some time before death stiffen very rapidly. When convulsions precede death, rigor mortis sets in early as a rule, but in certain cases, where death has been preceded by strong convulsions, rigidity may appear quickly, but last for some days, as in some cases of poisoning by strychnine.
Conditions which simulate rigor mortis:—
(1) Stiffening by Catalepsy.—In this condition the temperature of the body will remain at a degree compatible with life over a period incompatible with real death. If a limb be extended and rigid in catalepsy, after passive flexion of it, it will return to its former state.
(2) Rigidity from the Body being Frozen.—In this condition passive movement of the joints is accompanied by crackling due to fracture of their frozen contents.
(3) Heat Stiffening.—Is seen in the bodies of persons who have been suddenly immersed in boiling fluids; also to a certain degree in bodies of persons who have met their death by burning from paraffin lamp accidents.
Cadaveric Spasm or Instantaneous Rigor.—“When this phenomenon occurs the last act of life is crystallised in death.” It is a prolongation of the last vital contraction of the muscles into the rigidity of death. Cadaveric rigidity of the muscles must be distinguished from muscular spasm occurring at the moment of death.
They may thus he distinguished: In cadaveric rigidity any object placed in the hand prior to the onset of rigor mortis can be readily removed, even if the precaution be taken of binding it in the hand prior to the accession of rigor mortis.
In the case of muscular spasm the object is found grasped in the hand, and can only be with difficulty removed.