What is fever?

While fever has been recognized as an important symptom of disease for millennia, the role of the nervous system in its induction has only really been investigated seriously in the present century. But, before examining this role it is necessary to define fever and to discuss matters such as its survival value and how widespread its occurrence is in the animal kingdom.

Two terms are commonly used to refer to a rise in the temperature of the body core namely, hyperthermia and fever. For the purposes of this book I will refer to fever as a rise in core temperature occasioned by a pathological process, in which the raised core temperature is defended. This condition could include the fevers related to that usually ill-defined condition ‘stress’. Hyperthermia includes the condition of raised body temperature in the absence of a pathological process such as can be caused by immersion in a hot pool, or working in a vapour impermeable suit in the heat. The concept of a defended raised temperature, or raised set point, was clearly stated by Liebermeister, (1871). He wrote (in old German spelling): ‘Der wesentliche Unterscheid des Fieberkranken vom Gesunden besteht demnach weder in der höheren Körpertemperatur noch in der grösseren Wärmeproduction, sondern darin, dass Wärmeverlust und Wärmeproduction für einen höheren Temperaturgrad regulirt werden. Zum Wesen des Fiebersgehört, dass die Wärmeregulirung auf einen höheren Temperaturgrad eingestellt ist’.