Our sense of smell allows us to discriminate among five thousand to ten thousand odors. Some people can detect the odor molecules in a green bell pepper at a concentration of less than one part per trillion. That is like picking out one grain of sand from a mile-long beach. How do we do that? What we perceive as a smell is our brain’s response to a cocktail of molecules floating in the air. The molecules that we ultimately register as an odor are tiny, light enough to be suspended in the air. As we breathe or sniff, we suck these odor molecules into our nostrils. From there, the odor molecules
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