Pleasure, pain, and prophylaxis: olfaction (the neglected sense).

Results Mast cell degranulation C-fiber sensory nerve stimulation Other C-fiber sensory nerve Distant mast cell degranulation stimulation Ladies and gentlemen, you stink! Each of you has a unique, genetically determined odor. Your aroma is so unique that a trained dog can trace your path, undistracted by the myriad of smells with which your spoor has been mixed. The structure of chemosensory communication is wonderfully ancient: coelenterates, nematodes, arthropods, and mammals, including humans, identify themselves and their biologic status by chemistry—the release of specific chemicals into the local environs (1). All living creatures from the simplest algae or amoeba to highly sophisticated human beings identify themselves by chemicals which are recognized by specialized cells that constitute the olfactory system. Each human being has a unique identifying odor linked to his or her histocompatibility genotype. One of my mentors in medicine, Lewis Thomas, suggested 20 years ago that a bloodhound’s nose would be a more accurate method of selecting donors and recipients for organ transplantation than all of the laboratory testing. But no one has taken his suggestion seriously.