An electrophysiological investigation of the receptor apparatus of the duck's bill.

1. The properties of receptors in the duck's bill have been studied by recording from units isolated by dissecting fine filaments from the maxillary and ophthalmic nerves.2. The units studied were divisible into three groups, phasic mechanoreceptors responsive to vibration, thermoreceptive units, and high threshold mechanoreceptors.3. Vibration-sensitive mechanoreceptors (113 units) had small receptive fields, showed a rapidly adapting discharge to mechanical stimulation of the bill, were sensitive to vibratory but not to thermal stimuli and showed no background discharge.4. Temperature receptors (twenty-one units) were insensitive to mechanical stimulation and showed a temperature-dependent background discharge. Sudden cooling produced a transient increase in discharge frequency.5. High threshold mechanosensitive units (eight units) gave a slowly adapting discharge to strong mechanical stimulation and were insensitive to vibratory and thermal stimulation.6. It is concluded that the low-threshold, vibration-sensitive responses come from Herbst corpuscles. No specific function can yet be assigned to the Grandry corpuscles.