The form and distribution of the receptive fields of Pacinian corpuscles found in and around the cat's large foot pad.

1. Firing thresholds of Pacinian corpuscles situated within or close to the large pad of the cat's hind foot have been determined following step displacements applied to various points on the pad surface.2. The most sensitive positions on the receptive fields of thirty-one corpuscles were distributed unevenly over the pad. About half were situated close to the interlobular crease lines, and most of the others were at the edge of the pad.3. Threshold receptive fields were usually of complex form, with more than one region of low threshold.4. The approximate locations of a number of Pacinian corpuscles whose fields had been mapped were determined by dissection.5. The most sensitive position on the pad was usually at the closest point to the corpuscle. If the corpuscle was situated outside the pad itself, it was therefore usually most easily excited from some point at the edge of the pad. However, a minority of Pacinian corpuscles were most easily stimulated from some region other than that closest to them.6. It is suggested that previous estimates of the ability of this population of receptors to transmit information about the positions of stimuli (Gray, 1966) must be re-evaluated in the light of the non-uniform distribution and asymmetry of their cutaneous receptive fields.