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. 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_:--