The discharge of sweat in Welsh Mountain sheep

1. Experiments were done on Welsh Mountain sheep to determine whether the sheep can be caused to discharge sweat continuously. 2. On administration of sequences of four to eighteen I.V. injections of adrenaline or noradrenaline (200 μg), sheep responded to the first 4‐5 injections with decreasing amounts of sweat discharge. Thereafter, the responses were fairly constant at about 10% of the first discharge. Occasionally one injection within a series elicited no sweat discharge but on other isolated occasions large discharges of sweat were induced. The blood pressure response to repeated I.V. injections of adrenaline remained constant. 3. Inhalation of amyl nitrite or rebreathing of expired air during I.V. adrenaline injections had little effect on the pattern of intermittent sweat discharges and did not induce a continuous outflow of fluid from the sweat glands. 4. Continuous infusions of adrenaline and of carbachol did not cause a change in the rate of continuous water vapour loss from the skin but possibly increased the frequency of intermittent sweat discharges. 5. Electrical stimulation of the cervical sympathetic nerve for short (0·5–2 min) or long (20–30 min) periods caused only transient (3–6 min) increases in water vapour loss from the cheek skin. 6. None of these experiments indicated that the sweat glands of the sheep can be induced to discharge fluid continuously.