HOW DOGS SMELL: Dogs' noses are such sensitive chemical detectors that they can detect a target compound in the presence of other odors at much higher concentrations; they can even identify odors concentrated in a small object or piece of ground as small as a dime. They can even discriminate between a target odor and one that is closely related. Scent comes from an object in a plume that swirls and eddies so there are patches of dense odor and areas of faint odor. A dog will scan back and forth with its nose along those varying densities to try and locate the source of a smell.
IN ADDITION TO FINDING BED BUGS: Dogs have been used by law enforcement and military personnel for 30 years to detect narcotics and explosives because of their keen sense of smell. The Minnesota Protection Control Agency (MPCA) is now using specially trained dogs to check schools and other facilities for mercury contamination. The MPCA estimates that there is around two pounds of mercury "hidden" in most schools. The U.S. Environmental Protection Agency is also conducting research on how to use dogs for detection of indoor air pollutants such as toxic molds, illegal pesticides, and gasoline vapors from contaminated ground water.
INSIDE HUMAN NOSES: Our sense of taste is partially enhanced by smell, which is why food may taste bland when we have a cold that blocks the nasal passages. Nerve receptor cells within the nose detect odors carried into the organ by air, and transmit signals to the brain through the olfactory nerve.