Extremity heat loss in water in humans and macaques

Human hands and feet lose about the same amount of heat per unit time in cold water. This is somewhat strange since they are grossly different in size (volume). When corrected for size, the human hand loses far more heat per unit volume than the foot. This study attempted to see if macaques showed comparable hand‐foot differences by repeating the human test situation as closely as possible on 20 macaques. The monkeys lose less total heat in cold water because their hands and feet are so much smaller, but on a volume basis they exceeded human heat losses. Even more important, the macaque hand and foot show very similar heat losses when the size difference is removed. The human hand and the macaque hand and foot are reasonably close in heat loss per unit volume; the human foot appears unique. Another sample of human subjects in which both extremity volumes and surface areas were measured showed closer heat loss correspondence between hands and feet on the basis of surface area, but the human foot still was lower. Pedal heat loss in man is apparently conditioned by a combination of the foot's special morphology and vascularity.