surface temperature and 3) they are prone to low readings because it is not always evident that the surface thermal connection is adequate.
Body Surface Temperature
Heat signatures vary considerably over the surface of the human body, and physicians have long appreciated the relationship be- tween heat and disease. In fact as early as 400 BC, Hippocrates wrote “In whatever part of the body excess of heat or cold is felt, the disease is there to be discovered.”1 Undoubtedly the earliest use of clinical ther- mography, Hippocrates found when he cov- ered his patient’s body with wet clay, the mud dried quicker on the diseased area, thus pre- senting a crude but dramatic demonstration of the heat signatures.
It is impossible to define the surface tem- perature by any single normal value, since it is the result of a thermal balance between energy supplied from the core via perfusion
and energy lost to the environment via radiation, conduction, convec- tion, and evaporation. All objects, whether animate or inanimate, ho- meothermic or poikilothermic, radiate electromagnetic energy (radia- tion) to the surroundings at a rate dependent on its temperature. In accordance with a basic law of physics, this invisible radiation is con- stantly emitted, absorbed, and
If the human eye had the optical power to see the emitted radiation, which has all the same properties as a beam of light, but differing in wavelength, all mankind would have an incandescent glow. Because the temperature over the surface of the human body changes at a rapid rate in response either to its external environment or to its internal con- trol mechanism, the incandescence would be quite bright over some areas and quite dark over others. This variability of the temperature pattern gives question as to its significance, and yet it is a remarkable indication of the underlying body physiology.
All biological tissue generates energy in proportion to the metabolic ac- tivity occurring within the cells. About 80% of the energy developed by
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