1. The heat emission of two closely clipped sheep was studied in forty experiments in which three feeding levels were employed and in which environmental temperatures ranged from 8 to 38° C.

2. The sheep shivered at temperatures below 23° C., but the first reaction to cold was a corrugation of the skin referable to contraction of the fascial muscles.

3. As environmental temperature increased voluntary water consumption and urinary volume increased markedly. Only a small degree of cooling resulted from this warming of large quantities of water through a relatively small temperature gradient.

4. The basal loss of heat by vaporization of water was 316 Cal./m.2/24 hr. in one sheep (3) and 307 Cal./ m.2/24 hr. in the other (23). Increased vaporization occurred at environmental temperatures of 31° C. for the experiments at the low-feeding level, 27° C. at the medium level and 26° C. at the high level. The water-vapour loss increased subsequently by 87 Cal./m.2/24 hr./° C. change in environmental temperature in sheep 3 and by 88 Cal./m.2/24 hr./° C. in sheep 23. Respiratory frequencies increased with increasing heat loss by vaporization. Some evidence suggests that when the water-vapour loss was high the excretion of potassium through the skin was increased.