The key experiment for his receptor concept involved the antagonism between nicotine and curare and was carried out on an anaesthetized rooster. Injection of nicotine led to a characteristic contraction of certain muscles of the leg, recognizable in the stiff, extended legs of the animal. This effect could be antagonised by injecting curare, resulting in the relaxation of the leg muscles. This antagonism could also be shown if the relevant nerves of the leg muscles had been cut through and allowed to degenerate, which meant for Langley that the two drugs acted on the muscle tissue directly. Just like pilocarpine and atropine, nicotine and curare competed for the same substances in the protoplasm of the cells. Moreover, after application of curare the relaxed leg muscles could be made to contract by applying an electric current. Langley concluded from this finding that neither the drugs nor the electric stimulus acted directly on the contractile substance of the muscle cells, but on what he called ‘accessory substances’. And, he continued, ‘Since this accessory substance is the recipient of stimuli which it transfers to the contractile material, we may speak of it as the receptive substance of the muscle [15]’.