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1. The effects of blocking agents on the responsiveness of the cast' pad and human forearm sweat glands have been studied. 2. Of the anti-adrenergic substances examined (dibenamine, phenoxybenzamine, bretylium, guanethidine and phentolamine) only high doses of guanethidine and phentolamine produced any consistent and significant measure of blockade, and small doses of atropine were as effective as these large doses of guanethidine or phentolamine. 3. It is concluded from the blockade of chemical stimulation as well as transmission by these substances that (1) there are only cholinergic fibres innervating eccrine sweat glands, and (2) any inhibitory action by anti-adrenergic substances is due to interaction with cholinergic receptors in the glands.

1. The influence of repeatedly raising the body temperature by radiant heat to a level at which acclimatization to heat is normally acquired was investigated in two series of experiments, the first without the subjects sweating, the second with sweating. 2. In a second investigation local sweat-gland activity was induced by drug injections on successive days without raising the body temperature. 3. These experiments show that the increased sweating capacity characteristic of acclimatization to heat is a result of sweat-gland activity and does not appear to be induced by or to depend on an elevated body temperature. 4. Secretory activity results in a loss of glycogen from sweat-gland cells on the first day of heat exposure but not after the glands have been ‘trained’ by acclimatization to heat. 5. The state of acclimatization has no influence on the threshold concentration of acetylcholine required to elicit sweating when injected intradermally.