Toxicology identifies substances in the body; pathology determines cause and manner of death. Together, these disciplines are essential for understanding how and why a person died.
Forensic pathology is a branch of medicine that applies the principles of pathology to legal investigations of death. A forensic pathologist — often called a medical examiner or coroner (depending on jurisdiction) — is responsible for determining the cause of death (the disease, injury, or mechanism) and the manner of death (the circumstances under which the cause arose).
The autopsy (also called a post-mortem examination) is the primary tool of the forensic pathologist. It typically involves three stages: external examination — documenting injuries, identifying marks, and noting the general condition of the body; internal examination — systematic dissection of body cavities and organs to identify disease processes, injuries, or abnormalities; and sample collection — obtaining blood, urine, vitreous humor, organ tissue, and other specimens for toxicological and histological analysis.
In most medicolegal systems, the manner of death is classified into one of five categories: natural (resulting from disease or internal malfunction), accident (unintentional injury), suicide (self-inflicted with intent to die), homicide (death caused by another person), or undetermined (when the circumstances cannot be conclusively established).
Estimating the time of death (also known as the post-mortem interval) is one of the most important — and most challenging — tasks in forensic investigation. Pathologists rely on a combination of physical and chemical changes that occur in the body after death.
Algor mortis refers to the cooling of the body after death. Under standard conditions, the body loses heat at a rate of approximately 1.5°F (0.83°C) per hour until it equilibrates with the ambient temperature. The rate is affected by body mass, clothing, environmental temperature, and whether the body is submerged in water or exposed to wind.
Rigor mortis is the stiffening of muscles after death, caused by the depletion of adenosine triphosphate (ATP) and the formation of permanent cross-bridges between actin and myosin filaments. It typically becomes noticeable 2–6 hours after death, fully develops by approximately 12 hours, and gradually dissipates over the next 24–48 hours as muscle proteins begin to break down through autolysis.
Livor mortis (also known as lividity) is the settling of blood in the lowest parts of the body due to gravity once circulation ceases. It appears as a reddish-purple discoloration, becoming visible within 1–2 hours of death. In the early stages, lividity is unfixed — pressing on the discolored area will cause it to blanch. By approximately 8–12 hours post-mortem, the lividity becomes fixed as blood coagulates in the tissues. The pattern of lividity can indicate whether a body has been moved after death.
Decomposition progresses through five recognised stages: fresh (immediately after death, internal autolysis begins); bloat (gases produced by bacterial activity cause swelling); active decay (tissue breakdown accelerates, significant mass loss); advanced decay (most soft tissue has been removed); and skeletal (only bones, cartilage, and dried skin remain). The rate of decomposition depends on temperature, moisture, insect access, and burial conditions.
Quick Check
In what order do the three post-mortem changes typically appear?
Fill in the Blank
The stiffening of muscles after death, caused by the depletion of ATP, is called________.
Forensic toxicology is the study of the detection and identification of drugs, poisons, and other chemical substances in biological specimens — and the interpretation of their role in causing or contributing to death, impairment, or injury. It draws on analytical chemistry, pharmacology, and clinical medicine.
Toxicological analysis can be performed on a range of biological samples. Common specimens include blood (the primary specimen for quantitative drug analysis), urine (useful for detecting drug metabolites over a longer window), vitreous humor (the fluid inside the eye, resistant to decomposition and contamination), hair (can reveal chronic drug use over weeks to months), and liver tissue (a site of drug metabolism and accumulation).
Forensic toxicology employs a two-stage analytical approach. Screening is performed first using immunoassay techniques, which can rapidly detect broad classes of drugs and toxins. However, immunoassays can produce false positives due to cross-reactivity with structurally similar compounds. Confirmatory testing is then carried out using gas chromatography–mass spectrometry (GC-MS) or liquid chromatography–tandem mass spectrometry (LC-MS/MS). These instruments separate complex mixtures into individual components and identify each by its unique mass spectrum, providing definitive identification and precise quantification.
“The dose makes the poison. There is no substance that is not a poison; it is only the dose that distinguishes a poison from a remedy.”
— Paracelsus (1493–1541), considered the father of toxicology
| Substance | Source | Detection Method | Symptoms |
|---|---|---|---|
| Carbon monoxide | Combustion (fires, engines) | CO-oximetry | Cherry-red lividity |
| Cyanide | Industrial / natural sources | Blood cyanide test | Bitter almond odor |
| Arsenic | Contamination / pesticides | ICP-MS / hair analysis | GI symptoms |
| Ethanol | Alcoholic beverages | Blood alcohol test | CNS depression |
Quick Check
What confirmatory analytical technique is most commonly used in forensic toxicology?
Fill in the Blank
The ancient principle that 'the dose makes the poison' is attributed to________, considered the father of toxicology.
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