Thanatology — Signs of Death, Rigor, Livor and Algor Mortis, Putrefaction and Adipocere

Thanatology is the branch of forensic medicine that deals with death and the changes that follow it. Its practical purpose is to estimate the time since death (TSD), also called the post-mortem interval (PMI), and to help establish the cause and manner of death. Post-mortem changes depend on ambient temperature, season, body fat, sepsis or injuries, intoxication and clothing or insulation.

• Cessation of respiration — assessed by auscultating over the upper lung fields.
• Cessation of circulation — absent heart sounds over the precordium; a persistently flat ECG supports cardiac arrest alongside clinical findings.
• Cessation of nervous-system function — absent brainstem reflexes; EEG activity absent.
• Insensibility and loss of voluntary movement — among the earliest signs.
• Primary muscle relaxation — the immediate loss of tone.

Skin and eyes. Within minutes the skin turns pale and ashen and loses elasticity, and the lips dry and harden. The cornea becomes opaque and pupillary and corneal reflexes are lost. Loss of intraocular tension makes the eyeball flaccid. In an eye left open, dust, debris and mucus form a yellow triangular area on the exposed sclera that darkens to brown-black: tache noire de la sclérotique. Segmentation of retinal vessels (the Kevorkian sign) is described but of limited forensic value. Vitreous humour potassium rises steadily after death.

Algor mortis is post-mortem cooling. Heat production stops with circulation, and the body loses heat down the gradient to its surroundings — first mainly by radiation, later by conduction and convection. StatPearls describes algor mortis as the most accurate method of estimating time since death in the early period, and notes a rule of thumb of about 1.5 degrees Fahrenheit fall per hour. Henssge's nomogram is the most widely taught method.

Rigor mortis is post-mortem stiffening of muscle caused by ATP depletion. After death, loss of membrane integrity lets calcium into the fibres and actin and myosin bind. Relaxation needs ATP to pump calcium back into the sarcoplasmic reticulum and to detach the actin–myosin complex; without ATP the cross-bridges stay locked and the muscle stiffens. Primary relaxation comes first; secondary relaxation follows when putrefaction breaks down the contracted muscle, at roughly 36 hours.

• Rapid onset and early resolution — children, the elderly, and deaths with severe exhaustion (for example cholera) or convulsions (for example strychnine).
• Cutis anserina (goose skin) — contraction of the erector pili.
• Cardiac rigor — ventricular contraction that can be misread as hypertrophy.
• Dartos contraction — wrinkled scrotal skin; with contraction of the seminal vesicles and vas deferens it can cause post-mortem seminal emission, which must not be taken as proof of ante-mortem sexual activity.

After circulation stops, blood settles under gravity into dependent areas, producing reddish-blue discolouration — livor mortis, lividity, hypostasis or post-mortem staining. In a supine body it appears over the back.

• Shifting: if the body is turned within the first hours, blood redistributes to the new dependent areas.
• Blanching test: press with the thumb for about 1 minute; pallor on release means lividity is not fixed, persistent colour means fixed.
• Contact pallor (contact flattening): areas pressed against the floor, bed or slab, or under tight clothing or bands, stay pale because compressed vessels cannot fill.
• Intensity: reduced after major blood loss or anaemia, increased in asphyxial deaths.

Autolysis is self-digestion by the body's own enzymes after cell membranes break down; it does not need bacteria. Its earliest external sign is a whitish cornea. Autolysis in the fetus within the amniotic cavity is maceration (skin slippage with blackish-brown discolouration). Putrefaction is microbial decomposition. The principal organism is *Clostridium perfringens*, a Gram-positive anaerobic rod whose lecithinase lyses red cell membranes; hydrogen sulphide from bacterial metabolism combines with haemoglobin to form sulphaemoglobin, giving the green colour.

These are the two modifications of putrefaction, produced by very different conditions. Both preserve facial features and injuries, so identification and injury recognition remain possible.

• First sign of putrefaction — green discolouration over the right iliac fossa.
• Earliest sign of autolysis — whitish cornea.
• Rigor mortis mechanism — depletion of ATP, so actin and myosin cannot detach.
• Livor fixation — about 6 to 8 hours, with the blanching test.
• Cadaveric spasm — instantaneous, helps manner of death.
• Adipocere vs mummification — warm moist vs dry arid.
• Casper's dictum — decomposition is twice as fast in air as in water and 8 times as fast as in soil (8 : 4 : 1).
• Poison and lividity colour — cherry red (CO), pink (cyanide), brown (nitrate).