Here, the only difference between these molecules is the number of carbon molecules and their paired hydrogen atoms. Alkanes with a low molecular weight don't smell, however, those with larger molecules have a distinct gasoline-type odor.
Most people can smell alkanes (unless they have a heavy cold and a bunged up nose). It, therefore, seems obvious that dogs can smell alkanes. And yes, this is indeed the case. But there's a twist.
A dog's sense of smell is so sensitive that they can detect tiny amounts of an alkane, such as a few parts per trillion. And here's a thing - people with cancer tend to release micro amounts of alkanes on their breath. If a dog was able to detect these tiny amounts, then it would make for one awesome way of diagnosing early-stage cancer in a non-invasive way.
Guess what! Dogs have the scent capacity to do just this.
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Signs a Dog can Smell an Alkane
Taking the last point first, these trained detection dogs are taught to react in a way that doesn't alarm the patient. Thus, if such a dog smelled alkane on a patient's breath, it's most likely they will be trained to lie down quietly. This alerts the handler the dog has identified a positive case, but without alarming the person.
In more general terms, if a dog was following a scent trail to a source of hydrocarbon fuel, the dog shows more general scanning and sniffing behavior. This includes the dog scenting the air and moving rapidly forward toward the source of the odor. The dog takes rapid, shallow sniffs, often moving their head from side to side. This helps the dog detect the strongest concentration of scent molecules and move toward it.
As the dog nears the target scent, they slow down. Nose to the ground, the dog takes deeper, less frequent breaths. This allows the dog to better process the scent and decide how fresh it is while looking for scent clues as to the nature of the source of the smell.
- Wag tail
- Lips pushed forward
- Lying down
- Scenting the air
- Nose to the ground
A History of Dogs Detecting Alkanes
Detection dogs are also used for more positive purposes, such as search and rescue, and are able to find bodies trapped under rubble. Then, in the 21st century, the idea of cancer detection dogs was born. Dogs have the ability to detect alkane molecules in just a few parts per trillion. Thus, it was reasoned they should be able to detect alkane molecules released as a result of lung cancer - on the patient's breath!
A study by the Pine Street Foundation, California conducted a controlled trial into just this. They found dogs were indeed able to detect early-stage lung cancer with a 99% success rate.
The Science of Dogs Sniffing Out Alkanes
To start with, a dog's moist nose traps scent molecules to better offer them up to the scent-detecting cells inside the nasal chamber. Once inside the nose, the surface area of olfactory (scent) cells is anything from 35 - 75 times greater in a dog (depending on breed) than in a human.
Once the olfactory cells are triggered, messages are passed for processing to the olfactory center in the brain. Again, in the dog, this is significantly larger, which enables them to pick up smells that are undetectable to people. Hence, a dog can smell alkanes on the breath of a cancer patient, which a human would not be able to detect.
Training a Dog to Detect Alkanes
Once a promising candidate is identified, their training starts with a simple game of tug. Using a laundered towel (so that it is free from extraneous scents), the dog is engaged in a game of tug. The dog is praised and rewarded for engaging enthusiastically in the game. This is repeated on lots of occasions so that the dog has great fun and links the towel to tug.
A second towel is now introduced. This new towel is impregnated with a small amount of alkane smell. The two towels are placed beside each other and the dog is invited to play tug. If they select the non-smelly towel, the handler ignores them. When they select the alkane-infused towel, the handler engages in an active and enjoyed game of tug.
Once the dog is regularly selecting the alkane-infused towel, then yet more clean towels are introduced. Each time, the dog is only rewarded when they select the alkane one. The next step is to hide the alkane towel and only reward the dog when they sniff it out and find it.
This game of hide-and-seek starts out easy, with the towel simply behind an obvious object. As the dog's skills develop, so the hiding place is made more obscure so the dog has to use their nose to sniff it out and find it, all to get their reward.
How to React to a Detection Dog Sniffing Out Alkanes:
Never interrupt a sniffer-dog while they are working. Always speak to their handler in the first instance, and ask if it's OK to approach the dog or not.