When this irritability
ceases--and it seldom exceeds two hours--rigidity and hardening sets in,
and in _all_ cases precedes putrefaction. It is caused by the
coagulation of the muscle plasma. It commences in the muscles of the
back of the neck and lower jaw, and then passes into the muscles of the
face, front of the neck, chest, upper extremities, and lastly to the
lower extremities.

It has been noticed in the new-born infant, as well as in the foetus. It
lasts from sixteen to twenty hours or more. In lingering diseases, after
violent exertion, and in warm climates, it sets in quickly, and
disappears in two or three hours; in those who are in perfect health and
die from accident or asphyxia, it may not come on until from ten to
twenty-four hours, and may last three or four days. After death from
convulsions or strychnine-poisoning, the body may pass at once into
rigor mortis. Rigor mortis must be distinguished from _cadaveric spasm_
or the _death clutch_; in the former, articles in the hands are readily
removable, in the latter this is not the case. In tetanic spasm the
limbs when bent return to their former position; not so in rigor mortis.

=Putrefaction= appears in from one to three days after death, as a
greenish-blue discoloration of the abdomen; in the drowned, over the
head and face. This increases, becomes darker and more general, a strong
putrefactive odour is developed, the thorax and abdomen become distended
with gas, and the epidermis peels off. The muscles then become pulpy,
and assume a dark greenish colour, the whole body at length becoming
changed into a soft, semi-fluid mass. The organ first showing the
putrefactive change is the trachea; that which resists putrefaction
longest is the uterus. These putrefactive changes are modified by the
fat or lean condition of the body, the temperature (putrefaction taking
place more rapidly in summer than in winter), access of air, the period,
place, mode of interment, age, etc. Bodies which remain in water putrefy
more slowly than those in air.

=Saponification.=--In bodies which are very fat and have lain in water
or moist soil for from one to three years this process takes place, the
fat uniting with the ammonia given off by the decomposition to form
_adipocere_. This consists of a margarate or stearate of ammonium with
lime, oxide of iron, potash, certain fatty acids, and a yellowish
odorous matter. It has a fatty, unctuous feel, is either pure white or
pal