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The canine nose has something like twenty times as a lot of necessary receptor cells as the humane nose. How all of this works to detect odors is one of the colossal scientific wonders of the earth. Studies in a number of species own inaugurate that dissimilar regions of the mucous lining within the nose own dissimilar chemical properties , more readily absorbing chemicals of one particular molecular form or another , or preferentially absorbing in one region chemicals that are more water soluble and in another chemicals that are more buxom soluble.

The ability of the nose to shape precise chemical distinctions is genuinely extraordinary. Some pairs of chemicals that exist in nature are identical in every way - they are made up of precisely the same elements , joined together in precisely the same three-dimensional series - accept that one is the three-dimensional mirror image of the other. Yet such "stereoisomers" many times own a dramatically dissimilar odor , indicating that the nose can sort them out by their complex form alone. The molecule carvone , for specimen , has the odor of caraway in one of its stereoisomers , the odor of oil of spearmint in its mirror-image form.

Measurements of the acuity of the dog's nose suggest that the dog is a lot of times more touchy than man to the presence of minute quantities of odor molecules wafting in the air , but the selective information are all over the map. This is probably in fraction because the threshold for detecting dissimilar chemicals no doubt varies dramatically according to the particular chemical involved. Some comparative studies own inaugurate that dogs can detect sure organic chemicals at concentrations a hundred times fewer than persons are competent to; for other compounds the dog's limit can be a element of a million or more. In police and security drudgery , dogs can detect the odor from natural gas leaks , concealed narcotics , explosives , and currency , all at levels opportunely below the threshold at which humans are aware of the odor.

In controlled studies dogs could detect humane savor on a glass slide that had been lightly fingerprinted and then left outdoors for as much as two weeks , or indoors for as much as a month; they could select which of six identical steel tubes had been held in the hands of a person for no more than five seconds; they could discriminate between T-shirts worn by two identical twins who ate dissimilar foods , or by two nonidentical twins who lived in precisely the same environment and ate precisely the same foods.

More than such a remarkable sensitivity to tip odors , it is the ability to select out particular odors of interest from a welter of competing smells and to match and discriminate them that is the dog's most impressive olfactory feat. This ability is surely a reflection of the dog's superior olfactory computing powers , for it requires not apparently smelling but analyzing. Dogs own no congenital interest in the savor of persons , narcotics , or hundred-dollar bills; but provided trained repeatedly to focus on sure categories of smells , they can do mind-boggling feats of cross-matching.