200 million scent receptors in the dog olfactory system help sniff out drugs and explosives, locate termites, gas pipeline leaks, and other things you may not know about.
Jobs for the Canine Nose
The canine’s extraordinary sense of smell serves humans in many ways. Most people know about dogs who track missing people and about drug-sniffing dogs who search out explosives, guns, and other contraband as well as cadaver material. According to the Alabama Cooperative Extension System, US Customs and Border Protection employs more than 800 canine teams that work with the US Dept of Homeland Security. Its Canine Enforcement Program uses a variety of breeds including German Shepherds, Labrador Retrievers, mixed breeds, and the celebrated Beagle Brigade to detect prohibited items at ports of entry.
However, these nasal powerhouses also help us locate gas pipeline leaks, water leaks, building molds and winery molds, endangered species, termites, bedbugs, weeds that are hazardous to agriculture, and fruits and vegetables that may ship dangerous insects and diseases into the country. Medical research even indicates that cancer sniffing dogs may be useful in identifying cancerous tumors.
How the Dog Nose Works
The canine olfactory system consists of soft tissue, bones, nerves, and parts of the brain. The soft tissue and bony structures make up the cavities into which odor particles flow. These cavities are lined with scent receptor cells which connect to olfactory nerves that connect with the olfactory lobe of the dog's brain.
Dogs have large folds of mucous membranes inside their nose containing more than 200 million scent receptors compared to smaller areas of mucous membranes containing about 5 million in humans. Their olfactory bulbs are also about 4 times larger than ours. However, some breeds are better suited for scent work than others. Longer muzzled dogs have more scent receptors than do short nosed dogs such as the Pug and Pekingese. The long ears of dogs such as hounds tend to scoop up more scent particles. Even more scent is caught up in the wrinkles of breeds like the Bloodhound.
According to Dr. Gary Settles, professor of mechanical engineering at Penn State, when a dog sniffs, he uses a different route of airflow than for normal breathing. A structure just inside the nostrils called the alar fold, opens allowing air to flow through the upper area of the nasal passages. A bony pocket traps odor molecules and they are dissolved in the mucous covered scent receptors where signals of this chemical change travel from the receptor along the olfactory nerve to the olfactory bulb at the end of each nasal passage.
When the dog exhales, the alar fold closes off the upper part and pushes air down and out through the slits on the side of the nose, which stirs up even more scent particles.
Odor molecules emanate from the source in a cone shape. Depending on environmental factors, odor molecules will be denser at the source and thinner as they disperse into the air. Scent detection dogs will scan this scent cone as they trail the source, often making a ‘whuffing’ sound.
Training and Accuracy
Training for scent detection dogs is kept positive and fun. These dogs consider their job a game. Depending on training and experience of the dog, skill of the handler, and a number of environmental factors, accuracy rates may range from 60% to 95%.
Sources:
Cadaver Dog Handbook by Andrew J. Rebmann, Marcella H. Sorg, Edward David
