A Natural History of the Senses

Introduction

• There is no way in which to understand the world without first detecting it through the radar-net of our senses. We can extend our sense with the help of microscope, stethoscope, robot, satellite, hearing aid, eyeglasses, and such, but what is beyond our senses we cannot know. Our sense define the edge of consciousness, and because we are born, explorers and questors after the unknown, we spend a lot of our lives pacing that windswept perimeter.
• Our sense connect us intimately to the past, connect us in ways that most of our cherished ideas never could.

The sense don't just make sense of life in bold or subtle acts of clarity, they tear reality apart into vibrant morsels and reassemble them into a meaningful pattern. They take contingency sample. They allow an instance to stand for a mob. They negotiate and settle for a reasonable version and make small, delicate transactions. Life showers over everything, radiant, gushing. The senses feed shards of information to the brain like microscopic pieces of a jigsaw puzzle.

• When we describe ourselves as "sentient" beings, we mean that we are conscious. The more literal and encompassing meaning is that we have sense perception.

Smell

• We can detect over 10k different odors, so many, infact, that our memories would fail us if we tried to jot down everything they represent.
• Smell is the mute sense, the one without words.
• Each day, we breathe about 23,040 times and move around 438 cubic feet of air. It takes us about five seconds to breathe - two seconds to inhales and three second to exhale - and in that time, molecules of odor flood through our systems,. Inhaling and exhaling, we smell odors. Smells coat us, swirl around us, enter our bodies, emanate from us. We live in a constant wash of them. Still when we try to describe a smell, words fail us like the fabrications they are. Words are small shapes in the gorgeous chaos of the world.
• Smell is the most direct of all our senses. When I hold a violet to my nose and inhale, odor molecules float back into the nasal cavity behind the bridge of the nose, where they are absorbed by the mucosa containing receptor cells bearing microscopic hairs called cilia. 5m of these cells fire impulses to the brain's olfactory bulb or smell center. Such cells are unique to the nose. If you destroy a neuron in the brain, it's finished forever; it won't regrow. If you damage neurons in your eyes or ears, both organs will be irreparably damaged. but the neurons in the nose are replaced about every 30 days and, unlike any other neurons in the body, they stick right out and wave in the air current like anemones on a coral reef.
• When the olfactory bulb detects something - during eating, sex, an emotional encounter, a stroll throught the park - it signals the cerebral cortex and sends a message straight into the limbic system, a mysterious, ancient, and intensely emotional section of our brain in which we feel, lust, and invent. Unlike the other senses, smell needs no interpreter. The effect is immediate and undiluted by language, thought, or translation.
• All smells fall into a few basic categories, almost like primary colors:
  • Minty (peppermint)
  • Floral (roses)
  • Ethereal (pears)
  • Musky (musk)
  • Resinous (camphor)
  • Foul (rotten eggs)
  • Acrid (vinegar)
• For centuries, people tormented and sometimes slaughtered animals to obtain four glandular secretions:
  • Ambergris (an oily fluid from the stomach of sperm whales)
  • Castoreum (from the abdominal sacs of Canadian and Russian beavers, and used by them to mark territories)
  • Civet (a honeylike secretion from the genital area of the nocturnal carnivorous Ethiopian cat)
  • Musk (a red, jellylike secretion from the gut of an East Asian deer) Because animal musk is so close to human testosterone, we can smell it in minuscule proportions.
• We need only 8 molecules of a substance to trigger an impulse in a nerve ending, but forty nerve endings must be aroused before we smell something. Not everything has a smell: only substances volatile enough to spray microscopic particles into the air.
• We taste only four flavors: sweet, sour, salt, and bitter. That means that everything else we call "flavor" is really "odor".
• Smell was the first of our senses, and it was so successful that in time the small lump of olfactory tissue atop the nerve cord grew into a brain. Our cerebral hemispheres were originally buds from the olfactory stalks. We think because we smelled.
• Our blood is mainly salt water, we still require a saline solution (salt water) to wash our eyes or put in contact lenses, and through the ages women's vaginas have been described as smelling "fishy".
• Each person has an odor as individual as a fingerprint. A dog can identify it easily and recognize its owner even if he or she is one of a pair of identical twins.
• A human has 5m olfactory cells, but a sheepdog has 220m and can smell 44x better than we can.
• Over time, smell has become the least necessary of our senses, "the fallen angel;" as Hellen Keller dramatically calls it.
• We're aware of smell, but we don't automatically react in certain ways because of it, as most animals would.
• Our sense of smell weakens as we get older, and it's at its peak in middle age. Alzheimer's patients, often lose their sense of smell along with their memory (the two are tightly coupled); one day Scratch-and-Sniff tests may help in diagnosis of the disease.
• Females score higher than males in sensitivity to odors, regardless of age group.
• If smell is a relic, it's of a time of great intensity, need, instinct, and delirium, a time when we moved among the cycles of Nature as one of its promising protégés. Except to taste and to sc out danger, we don't really need smell any longer, but we will not let it go.

Touch

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Taste

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Hearing

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Vision

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Synesthenia

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Postscript

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