Forensic Medicine and Toxicology
What is tested
Forensic medicine is a small but high-yield domain, largely factual: timing of death, wound interpretation, asphyxial deaths, poisoning syndromes, and consent and negligence law.
Core rules
- Postmortem changes: rigor mortis begins in 1–2 hours, is complete by about 12 hours and passes off by 24–36 hours; livor mortis fixes by 6–8 hours.
- Hanging vs strangulation: hanging gives an oblique, non-continuous ligature mark above the thyroid cartilage with the knot at the nape; strangulation gives a horizontal, continuous mark at or below the cartilage.
- Wounds: lacerations show tissue bridges and abraded margins; incised wounds are longer than deep; stab wounds are deeper than long.
- Poisoning signatures: organophosphate - miosis, bradycardia, salivation, bronchorrhea (SLUDGE); carbon monoxide - cherry-red skin, raised carboxyhemoglobin; cyanide - bitter-almond odor, high venous oxygen; methanol - formic acid, optic neuritis, metabolic acidosis; lead - Burton line, basophilic stippling; arsenic - rain-drop pigmentation, Mees lines.
- Consent: valid consent needs age (18 years in India), capacity, adequate information and voluntariness.
Worked example
A young woman is found dead with an oblique, parchmentized ligature mark high in the neck and no other injuries. Reasoning: the oblique, high, discontinuous mark plus absent defense injuries favors suicidal hanging; a horizontal low mark with bruising would favor strangulation. The distinction determines manner of death, not just cause.
Traps
Reading a ligature mark without noting its direction and level; and forgetting that organophosphate poisoning kills by bronchorrhea, so atropine is titrated to drying of secretions rather than to pupil size.