Results of three experiments were as follows: 1. After a 3‐ma DC current of 10‐min duration through the palmar skin, skin potential (SP) basal level is reduced in negativity and the positive wave of the SP response eliminated with no change in sweating (Sw) or skin resistance (SR). This demonstrates that SP basal level and the occurrence of the positive wave are not dependent on Sw or SR. 2. Placing a potential between the SP electrodes to vary SP basal potential will produce variations in response wave form, amplitude and latency. An induced potential comparable to that used in SR recording will produce SP responses of large amplitude. This suggests that the SP and SR represent different aspects of the same physiological processes. The effects of a DC current through the skin and exsanguination can be overcome by varying the SP basal potential. These results further demonstrate that SP responses are a function of SP basal level. 3. After atropinization, SP and SR return to their initial levels faster than Sw. It is concluded that SP and SR are partially produced by a process separate from Sw. Methodology, Human, Palmar sweating. Skin resistance. Skin potential, Atropine, Cholinergic, Exsanguination, Electrophoresis. (R. C. Wilcott)

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The following five experiments are reported. After palmar sweating is abolished by atropine, the skin is easier to drill with a dental burr. This suggests that arousal sweating protects the skin against mechanical injury. Intracutaneous injection of acetylcholine or mecholyl at the forearm will produce skin potential (SP) effects of both negative and positive polarity and also a reduction in skin resistance (SR). This suggests that a cholinergic substance is involved in the production of SP and SR. Intracutaneous injection of mecholyl at the forearm will either lower or raise the pain threshold to a needle prick. A lowering of the pain threshold was associated with the presence of an SP negative effect and a rise was associated with an SP positive effect. It is concluded that the adaptive value of the cholinergic substance related to SP and SR is to modulate cutaneous sensitivity. The pain threshold to an electric shock can be lowered or raised by mecholyl injection. This may show that the pain threshold can be varied by mecholyl injection independently of its effects on sweating. Lowering of the electric shock pain threshold at the palm is associated with the appearance of both SP negative and positive responses. This further demonstrates a relation between SP activity and pain sensitivity but indicates that the direction of the change in the pain threshold is not dependent on SP response polarity.

A study was made of the skin potential (SP), skin resistance (SR), and sweating of the cat's foot pad. Since many of the variables studied had previously been investigated in humans, comparable data were obtained. The characteristics of SP and SR of the cat are similar to those of humans, except that in cats, SP responses have a shorter latency than SR responses, and variation of the SP basal potential resulting from induction of a voltage between the SP electrodes has no effect on the amplitude or wave form of SP responses. Dissociation produced by arterial occlusion and procaine injection around the nerve suggest that SP responses of the cat are innervated by different nerve fibers than those which lead to the sweat glands.

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