Algor mortis
Algor mortis refers to the cooling of the body following death, a significant process in forensic science used to estimate the postmortem interval (PMI)—the time elapsed since death. Upon death, a human body's temperature begins to decrease until it matches that of the surrounding environment. The study of algor mortis, along with rigor mortis (stiffening) and livor mortis (discoloration), provides critical insights for investigators trying to determine the time of death in homicide cases.
The Glaister equation is commonly applied to calculate the PMI, based on the assumption that body temperature drops at a rate of approximately 1.5 degrees Fahrenheit per hour. For example, a body temperature of 90.2 degrees Fahrenheit might indicate a death occurring roughly 5.5 hours prior. However, various factors can influence the rate of cooling, including ambient temperature, metabolic conditions at the time of death, clothing, and the presence of insulating body fat. Understanding these variables is essential for accurate assessments in forensic investigations.
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Algor mortis
DEFINITION: Cooling of the body after death.
SIGNIFICANCE: Because the temperature of the human body begins to cool at the moment of death, observation of algor mortis is one of the ways in which forensic scientists attempt to estimate the postmortem interval.
Investigators of homicides use various techniques to estimate the length of time since death, or the postmortem interval (PMI). It is likely that before the techniques employed by modern investigators gained wide acceptance, early hunters and gatherers distinguished the same stages of decomposition following death. Such stages include the fresh, bloat, active, and advanced decay stages, versus the stage at which remains become dry or skeletonized. However, the indicators that modern forensic investigators consider classic for suggesting PMI are those of algor mortis (cooling of the body), rigor mortis (stiffening of the body), and livor mortis (discoloration of the body from gravitational blood seepage).
Because decomposition reflects chemical processes and all chemical processes are temperature-dependent, the acquisition of many of the conditions noticed after death is affected by temperature. That is, higher temperatures generally speed chemical reactions, and lower temperatures slow them. In algor mortis (the term derives from the Latin words algor, meaning “coolness,” and mortis, meaning “death”), the body is expected to cool until its temperature matches that of the surrounding environment.
If a body cools at a uniform rate, the measure of its temperature decrease following death can assist in the accurate determination of the elapsed time since death. The formula used for making such an estimate, known as the Glaister equation, is based on the notion that a dead body is expected to lose 1.5 degrees Fahrenheit per hour. Because the metabolic processes associated with maintaining life among humans generate a normal body temperature of nearly 98.4 degrees Fahrenheit, the Glaister equation estimates the approximate postmortem interval in hours by subtracting the body temperature (measured in degrees Fahrenheit at the rectum or deep within the liver) from 98.4 degrees and dividing the result by 1.5. Thus, if a decedent’s temperature is found to be 90.2 degrees Fahrenheit at the time of the body’s discovery, the decedent would be suggested to have died approximately 5.5 hours earlier.
After death, a body cools through radiation, conduction, and convection. As a result, many physical factors can influence algor mortis. One of these is ambient temperature, or, more precisely, the difference between ambient and body temperatures. If, for example, a body were to be discovered in a warm sauna, it might not have cooled at all. Furthermore, the body temperature of the decedent might not have been normal at the time of death owing to the effects of exercise, illness, or infection. Additionally, the amount of subcutaneous fat present, the lightness or heaviness of any clothing worn at the time of death, and any number of insulating coverings can alter the rate at which a body might be expected to cool. Any such variables can alter the effectiveness of employing the Glaister equation to estimate the postmortem interval.
Bibliography
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Shrestha, Rijen, et al. "Methods of Estimation of Time Since Death." StatPearls, 30 May 2023, www.ncbi.nlm.nih.gov/books/NBK549867. Accessed 14 Aug. 2024.
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