Body Temperatures

Abstract

Warm-blooded animals have an extremely complicated spatial temperature field; furthermore, it is not time-constant. In accordance with the basic laws of heat flow, the external parts of the body have a lower mean temperature than do the internal parts; likewise, the temperature decreases in the longitudinal axis of the extremities, thus producing a radial and an axial temperature gradient (Burton, 1934; Brück and Hensel, 1953; Wissler, 1961, 1970; Brown, 1965). The situation is further complicated by the differing heat production of individual organs, by irregularities in geometric forms, by changes in insulation and evaporation, and by convective heat transport via the blood. Attempts have been made to distinguish between the core of the body and its shell; the former is defined as the homeothermic part of the body, and the latter as the remaining part, which participates more or less in the fluctuations of the external temperature. However, no clear-cut dividing line can be drawn between the two parts. In homeotherms, the core generally consists of the interior of the thorax and abdomen, the brain, and part of the skeletal muscles. Under moderate changes in ambient temperature, the shell has been calculated as comprising 20% (Du Bois, 1951) to 35% (Burton, 1935) of the human body. However, during marked chilling, the shell amounts to as much as 50% of the total body; this is equivalent to a mean layer thickness of 2.5 cm.