The influence of deep body and skin temperatures on thermoregulatory responses to heating of the scrotum in pigs.

1. The temperature on the surface of the pig's scrotum was increased by circulating water through a pad held over the scrotal surface while the animal was lightly restrained.2. At an ambient temperature of 25 degrees C there was no change in respiratory frequency even when the scrotum was heated to 42 degrees C, but peripheral blood flow did increase and body temperature fell. At 30 degrees C ambient temperature, respiratory frequency increased when the scrotum was warmed to 42 degrees C. At an ambient temperature of 32 degrees C, the frequency increased at a scrotal temperature of 40 degrees C and was even higher when the scrotum was 42 degrees C, but body temperature did not fall.3. At a constant ambient temperature the effect on respiratory frequency of heating the scrotum to a given temperature depended on the skin temperature of the trunk which was modified by means of a coat through which water was circulated.4. In a cold environment, heating the scrotum was accompanied by a fall in body temperature, the arrest of shivering and a decline in oxygen consumption.5. Cooling a thermode in the hypothalamus or over the spinal cord inhibited the increase in respiratory frequency and peripheral blood flow caused by heating the scrotum. Warming either thermode potentiates the effect of heating the scrotum.