Discusses the hunting-behavior of the dogs, as a result of an olfactory response. Dogs may have an acute olfactory sensitivity to the form of the tracks made by the quarry and follow the trail from heel to toe. Dogs are also very sensitive to differences of spatial position of olfactory stimuli. The smell substances deposited by different parts of the body differ specifically in stimulating quality. A dog's sense of direction is due to the trailing of ground smell substances. Dissipation of the smell substance is a complex process, it could be in different states of matter. Since the substance to be odorous must be gaseous, it cannot be assumed that the stimulus intensity is greater at a recently made track, since it may not have vaporized. (PsycINFO Database Record (c) 2006 APA, all rights reserved)