Post-Mortem Changes, Decomposition and Pathology
Post-Mortem Changes
The sequence
Somatic death is followed by cellular death as tissues lose oxygen. Algor mortis (cooling at roughly 1-1.5 degrees Celsius per hour, plateauing at ambient in about 18-24 hours). Livor mortis (hypostasis: dependent lividity from about 20-30 minutes, becoming fixed at around 6-12 hours). Rigor mortis (onset 2-4 hours, complete by about 12 hours, resolving by 24-36 hours), following Nysten's law: jaw and neck first, then the limbs, then the trunk. Autolysis follows, then putrefaction.
Post-mortem stain versus lividity
Hypostasis is blood within vessels and blanches on pressure. Post-mortem stain is haemoglobin leaked into tissue after vessel breakdown; it does not blanch and can appear in non-dependent areas. Once lividity is fixed, repositioning no longer redistributes colour.
Other changes
Desiccation of lips, eyes and fingertips; mummification in dry, moving air; adipocere (saponified fat) in wet, anaerobic conditions; and putrefactive colour change beginning in the right iliac fossa.
Traps and a rule of thumb
Questions swap the timings, claim livor always blanches, or confuse rigor with cold stiffening (cold stiffening affects the whole body at once, whereas rigor travels). Rule of thumb: jaw before toe on the way in, and jaw before toe on the way out - rigor appears and resolves in the same order.
Decomposition and Pathology
What happens and why
Autolysis is self-digestion by cellular enzymes; putrefaction is bacterial action, chiefly from the gut, spreading along vessels and lymphatics. Recognise the sequence: greenish discolouration of the right iliac fossa, spread across the abdomen, marbling along vessels, bloating and gas, purge from orifices, skin slip, liquefaction, skeletonisation. Temperature, body mass, clothing, cause of death and where the body lay all alter the rate - sepsis accelerates it, cold slows it.
Conditions that change your plan
Oedema and ascites need a stronger solution, generous drainage and vigilance for swelling. Emaciation needs a weaker solution and less drainage. Jaundice needs a bleaching and dye approach to reduce yellow staining. Sepsis and gas gangrene demand a stronger solution, hypodermic treatment of affected limbs and thorough cavity work. Decomposed bodies need higher strength, repeated treatment and honest expectations. Antemortem trauma, burns and pressure sores need local treatment.
Traps and a rule of thumb
Common errors: embalming an oedematous body with a routine solution and finding it wet; over-draining an emaciated body; ignoring a gangrenous limb because the arteries still inject; promising a normal appearance in advanced decomposition. Rule of thumb: the solution is written by the case, not by habit - sepsis, swelling and decomposition mean strengthen; wasting means weaken and slow down.