The tracking of people by trayned dogs is based on the recognition of Which Compounds in a sweat from feat?

Human odor, Animal odor, etc. depends on what they are tracking. Some dogs are better than others, for example the blood hound is the best tracker, but is slower than a shepherd. A blood hound can follow a trail that is a few days old, through water etc. While a shepherd is only usable while the trail is fresh, and seldom a decent tracker with old trails.