Abstract
All sizes of the chemosensory hairs on the labellum of the blowfly, Phormia regina, contain neurons which respond to chemical stimulation with diphasic impulses if the recording electrode is at the tip of the hair. The impulses are initially positive, then become negative and return to the base line. The negative phase can be abolished by the action of anesthetics (xylocaine, cocaine, procaine, chloral hydrate) and tetrodotoxin, an extract from the puffer fish. The negative phase is increased by strong salts, mechanical injury, and thermal injury, which also act to reduce or abolish the positive phase. Simultaneous recordings from the side and the tip of the hair show that both positive and negative phases appear first at the side. These results indicate that the impulse is initiated in or near the cell body at the base of the hair and under certain conditions is propagated antidromically up the dendrite to the tip.