Single C-mechanorecptor afferent units were examined by recording from fibres dissected from the saphenous nerves of cats anaesthetized with chloralose. The receptive fields, averaging 4 X 3 mm when 10-50 X threshold stimuli were used, were in the hairy skin of the leg and foot. 2. The extent and excitability of receptor terminals was tested by two-and three-point field studies. The excitability of terminals in one part of the field of a unit could be depressed without affecting the excitability of terminals elsewhere in the field. 3. The afferent units could be excited by both inward and outward movement of the stimulus probe, in appropriate conditions; that is, there was non-directional sensitivity. 4. After-discharge was found to depend on restorative movements of the skin, not on a persistence of the response of the receptor to the original movement. 5. The response to mechanical stimulation was slowly adapting with two time constants and the stimulus-response relationship was exactly described by a power function, with exponents ranging from 0-6 to 1-3. 6. The C-mechanoreceptors could be depressed by rapidly repeated or prolonged mechanical stimulation and the effect was confined to the excited terminals.
