a complex indicator of the thermal state of animals and man. It results from the complex relations between the heat produced by the organs and tissues and the transfer of heat between the organs and tissues and the environment. In man and homeothermic animals, the body temperature is maintained by specialized thermoregulatory mechanisms at temperatures ranging from 36° to 39°C; the body temperature in birds ranges from 40° to 42°C.
Physiological fluctuations in the body temperature occurring during a 24-hour period follow circadian rhythms; in man, the difference between the body temperature in the early morning and in the evening varies from 0.5°–1.0°C. The differences in temperature among the internal organs amount to several tenths of a degree. The difference between the temperatures of the internal organs, muscles, and skin may vary as much as 5°–10°C. This makes it difficult to determine the average body temperature, which must be known in order to ascertain the thermal state of the body as a whole.
Body temperature is measured with a thermometer, which is usually placed in the armpit, rectum, mouth, or ear. In poikilotherms (cold-blooded animals), the body temperature differs little from the ambient temperature, and in some species it exceeds the ambient temperature only during intensive muscular activity.
The lowering or raising of body temperature (hypothermia and hyperthermia) by several degrees disturbs the body’s vital processes and may result in cooling, hyperpyrexia, or even death. In many diseases, such as fever, the body temperature rises to a certain level and is regulated at the new level.
K. P. IVANOV