Abstract
Contact chemoreceptors on the mouthparts and legs of the blowfly Phormia regina that normally respond to aqueous solutions of sapid substances also respond to compounds in the gaseous state. Effective vapors include organic and inorganic acids and various unrelated nonpolar compounds. In general, the acids stimulate the salt receptor. Some nonpolar compounds stimulate the salt receptor while others inhibit it. Others stimulate the water, sugar, or "fifth" receptor. Differential action cannot be attributed to pH or solubility. Not all compounds that are irritating to mammalian mucous membranes or amphibian skin stimulate the contact chemoreceptors of the fly. Sensitivity to these vapors is a phenomenon analogous to the common chemical sense of vertebrates.