By Carol Beuchat PhD
The amazing olfactory abilities of the dog are well-known to any dog owner. With a sniff of the door jamb, my dog knows who is on the other side of the front door before I open it, he can locate one of his toys hidden in a drawer, and he heads straight for the person with treats in their pocket when we go to the dog park. We have made good use of this portable detection system to find lost children, locate bombs, detect cancer, and many, many other things. The dog's nose is truly remarkable.
Just as amazing as its sensitivity to odor is its design, which is much more complex that it might first appear. Inside the muzzle is a complicated system of passages, the turbinates, that both humidify the air and also direct it to the olfactory organ for scent detection. This design must accomplish both respiration and scenting as breathing and sniffing, respectively.
| Some new studies reveal that the nose is much more complicated than might be expected from its simple design. There are two front-facing nostrils, or nares, as well as slits along the bottom on each side. With some very clever experiments, researchers have shown that this design is no accident. They have been able to reveal how air flows in and out of the canine nose, and how its simple design improves scent detection. In fact, engineers can build better chemical sensing devices by learning a few things from the dog. Although dogs usually make very willing research participants, to achieve enough control to do replicate experiments, the researchers fabricated a model of the nose. They used information from high-resolution magnetic resonance imaging (MRI) and made a model nose using a 3D printer. |  |
Inside the model nose, a cylinder with a a piston moved air into and out of the nostrils to mimic inhalation and exhalation. A hot-wire anemometer sensed the air flow and could detect changes with a resolution of 1 millisecond. The flow characteristics of the fake nose were similar to those of a Labrador Retriever.
To determine the sensitivity of scent detection, they placed a "smell" source, a chemical called 2,4-dinitrotoluene (DNT), in a small tin with holes in the side to allow vapor to escape. They used sophisticated chemical sensors (ambient ion mass spectroscopy) to document scent detection.
Finally, to visualize the flows of air, they used high speed video and "schlieren imaging", which uses optical techniques to photograph density gradients in air flow, as well as "theater fog" for some demonstrations.
 Staymates et al 2016 |  Staymates et al 2016 |
What they found is fascinating. When the dog exhales, air is directed downwards and outwards. When the dog is sniffing a surface, the airflow from exhalation actually draws the odor from the object being scented towards the nose. This effectively extends the "aerodynamic reach" of the nose. The inspiration-expiration cycle during scent detection is repeated very quickly, about 5 times per second.
 Staymates et al 2016 |  Staymates et al 2016 |
The air flow patterns that result from the simple design of the dog's nose increase the efficiency of scent detection by 8 times over that for the steady "inspiration" used in scent detection devices. This is achieved simply by directing the exhaled air away from the source of the odor in a way that draws the scent towards the nose. In fact, the farther away the scent, the greater the advantage of the dog's nose over a commercial device with continuous inspiration; in one set of experiments, the dog's nose was 4 times better than the detector at a distance of 10 cm from the source of the scent, and 18 times better at a distance of 20 cm.
Using what they learned from the dog, these researchers were able to construct a "bioinspired" scent detector that "sniffs" instead of continuously drawing in air and directs the exhaled air in a way that draws in scent from the source to the intake. When the air intake was directly above the source of the scent (distance = 0 in the graph below), continuous "inspiration" was as good or better than sniffing. But as the scent source moved away, the advantage of sniffing got better and better.
Staymates et al 2016
Needless, to say, the results of this study should be of great interest to the military and in situations where efficient odor detection is critical. A simple alteration in the design of odor detection devices, inspired by the anatomy of the canine nose, can result in spectacular improvements in efficiency.
Now why didn't we think of that?
Be sure to check out the really cool videos below that show the airflow patterns during odor detection by the model dog nose. (All videos are from Staymates et al 2016)
You can learn more amazing things about dogs in ICB's online course,
The Biology of Dogs
The next class starts Monday, 4 September.
Sign up HERE!
The Biology of Dogs
The next class starts Monday, 4 September.
Sign up HERE!
REFERENCES
Staymates ME, WA MacCrehan, JL Staymates, and others. 2016. Biomimetic sniffing improves the detection performance of a 3D printed nose of a dog and a commercial trace vapor detector. Scientific Reports 6:36876; DOI: 10.1038/srep36876.
Staymates ME, WA MacCrehan, JL Staymates, and others. 2016. Biomimetic sniffing improves the detection performance of a 3D printed nose of a dog and a commercial trace vapor detector. Scientific Reports 6:36876; DOI: 10.1038/srep36876.
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Visit our Facebook Groups
ICB Institute of Canine Biology
...the latest canine news and research
ICB Breeding for the Future
...the science of animal breeding
