ABSTRACTThe following five experiments are reported.1After 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.2Intracutaneous 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.3Intracutaneous 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.4The 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.5Lowering 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.