Newton's Apple : Teacher Guide

How do dogs find people buried in an avalanche?
Do all dogs have the same sense of smell, or do dogs with bigger noses smell better than those with little noses?
People have used dogs to find things for centuries, but scientists still don't completely understand why dogs are so good at using their noses.
Why is this difficult to understand?

Overview

Imagine you're skiing the deep snow of a mountain pass when you hear a low rumble. The snow beneath you suddenly gives way. In a terrifying instant you realize you've been caught in an avalanche. A roaring sea of snow envelops you and you are buried under snow compacted as hard as concrete. Rescue must come fast. After only 30 minutes your chances of survival are 50 percent. If you are not equipped with an avalanche rescue beacon, your next best hope is a search-and-rescue (SAR) team working with avalanche rescue dogs. How can a dog pick up your scent through densely packed snow, recognize the scent as the important one, and then hone in on it? Part of the answer is the dog's olfactory system, which is 10,000 to 10 million times more sensitive than a human's. Dogs have about 220 million scent cells, compared to about 5 million in humans. Scent cells, or cilia, react to odor-carrying molecules that flow into noses. In dogs, these cells line the canine mucosa, a membrane at the rear of the snout which is folded so many times that, if smoothed out, it would be larger than the dog's body. When the hairlike cilia encounter an odor-carrying molecule, they trigger nerve cells that signal the dog's brain. It takes three to six years to teach a dog to track a human scent, for the dog must learn to pick up and follow an individual scent it hasn't smelled before, and do it in rough terrain amid distractions. The task is made more difficult when the victim is buried under an avalanche and has left no scent trail. Dogs can smell a buried person because our bodies constantly shed skin cells and give off odors in the form of gases. A person walking across the ground leaves these cells and odors in a scent trail the dog can follow. A person buried under snow leaves no such trail, but dogs use air scenting to smell the human odors, or gases, rising up through the snow. A dog searches an area until it finds the spot where the odors are strongest, then alerts rescuers by barking or digging. For dogs, tracking and searching is just a game. For the buried victim, it's a matter of life and death.

Activity

Many people believe dogs are the top smellers of the animal kingdom, although that has never been proven. Scientists do know that dogs smell much better than most animals, including humans. Researchers have also found that some dogs can smell better than others, even if they are of the same breed. How sensitive is your nose? Can you smell better than some other people? And how does your nose stack up against a dog's? To find out, try this smell sensitivity test. Materials

glass measuring cup like those used for cooking
bottle of white vinegar
distilled water
several clean, medium-sized glass jars
masking tape
markers

1. Fill one glass jar with pure water and another with vinegar. Label the jars with a piece of tape and a marker. The water should not have an odor, while the vinegar will have its typical, distinct odor. 2. Put 1/4 cup of vinegar in another jar, then add 21/4 cups of water and mix the solution. The ratio will be 9 parts water to 1 part vinegar. Label this jar #1. Can you smell the vinegar? 3. Pour 1/4 cup of that 9:1 water/vinegar solution from jar #1 into a jar labeled #2. Add another 2 1/4 cups of water. You've just reduced the concentration of vinegar by an order of magnitude, making it ten times weaker. Can you still smell the vinegar? 4. Repeat step 3, this time pouring 1/4 cup of the diluted solution from jar #2 into a jar labeled #3. Add 21/4 cups of water to jar #3 and mix. You've reduced the concentration of vinegar by another order of magnitude. Can you smell the vinegar? 5. Continue the process until no one in the group can smell the vinegar. Questions

At what dilution could you no longer smell the vinegar? Dogs can smell the vinegar down to about 10 dilutions, six or seven orders of magnitude weaker than humans. Why?
Did anyone with a cold or allergies have a harder time smelling the vinegar? Why?
There are some odors that some people can't smell at all, a condition called human specific anosmia. Is there anyone in your group who can't smell vinegar at all?

Resources

http://www.drizzle.com/~danc/avalanche.html

http://www.sarbc.org/sarbc/sar-sar.html

http://yellow.crc.ricoh.com/carda/

Avalanche Rescue

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Overview

Activity

Resources