Last week, we talked about different types of search-and-rescue dogs and their different skills and searching techniques. Before we start to look at the difficulties of finding a victim in the real world, it might be useful to look at the amazing capabilities of these animals. How can a bloodhound sense a few scent molecules and use that to find a lost child? Or how can a Labrador catch a single trace of a victim buried in an avalanche or from vast distances away? The answer is actually quite simple—the canine nose.
The key to a dog’s ability to smell is twofold—the number of olfactory receptors and the architecture of the nose. Dogs have approximately 220 million receptors, compared to our own 5 million. This allows them to detect odors 100,000 times less concentrated than humans. To manage this kind of sensory overload, twelve percent of the canine brain is dedicated to smell; by comparison, humans use one percent of their brain for the same purpose. A dog’s olfactory receptors even have the infrared capability to literally smell heat. The best way to sum it up is that dogs smell like humans see: individual smells, not an overall smell (conversely, humans smell like dogs see). Where a human smells chicken soup, a dog detects cooked chicken, onions, rice, herbs and spices.
Sniffing for a dog is not actually part of their normal breathing pattern; instead it is a series of short inhalations and exhalations. Air is forced upward into the olfactory recess (pictured above in khaki), separate from the main respiratory airflow path. Due to the recessed positioning and complex folds, scent molecules are not washed out upon exhalation which allows for a concentration of scent over time. Molecules are absorbed into the mucous membranes of the olfactory recess and come in contact with the receptor neurons, which, in turn, carry the signal to the brain. An additional special aspect of canine olfaction is the ability to smell in stereo. This allows them to directionally work a scent cone and to distinguish individual smells.
Next week we’re going to look at how dogs use their amazing olfactory sense to be able to follow scent through some of the hardest of terrains, all while being confounded by air currents, turbulence, daytime heating, nighttime cooling, water, and other obstacles.