by Guy Murchie
Most of the time a hunting bat emits from ten to twelve chirps or beeps each second at a pitch averaging 50,000 cps, but when he detects a moth, say, five feet away, his output suddenly accelerates as he closes in on it, reaching what's called a buzz of some 200 beeps a second, which greatly increases his accuracy until he snags it - the whole pursuit and capture taking a scant third of a second with the bat's beeps (recorded on film) looking as you will see in the next illustration. Many bats thus catch gnats or moths when they're plentiful at a rate of one or two per second, which includes time for a reasonable percentage of misses.
Although the bat cannot possibly be conscious of it himself, his brain determines the moth's direction by comparing the echo's arrival time at one ear with that at the other - while the range is sensed in the lapse between each pulse out and its echo back, neither interval exceeding a thousandth of a second when the prey is close. It is probably not possible for a human to visualize accurately the kind of awareness a bat must have of the shape, size and motion of a flitting moth or of twigs, wires and other obstacles in his path, all sensed in darkness through his ears, but his sonar is certainly attuned to his specific needs, the distance between the sound waves about a tenth of an inch (just right for a small twig or a bug) and the aural images of these details all conveyed to his brain in electrical impulses of the auditory nerve (just as visual images are conveyed electrically by the optic nerve), combining into a sensation so complete it must be mentally equivalent to a visual impression.
Indeed the reason these remarkable creatures are not really "blind as a bat" (as tradition would have it) is not because they have eyes (which they all do) but because they have ears. For their ears give them what amounts to vision. In fact it has been proven experimentally that bats can fly with their eyes taped shut, but they cannot fly when their ears are plugged. So, in effect, they "see" with their ears. It is almost as if you had hundreds of ears, each one unbelievably sensitive to the exact direction of any sound you heard and that, while blindfolded, you listened to an orchestra until you could visualize the position and instrument each member was playing, all instantaneously, continuously and automatically in three dimensions, so that you could see the whole orchestra in action. Even if you can't imagine your hearing getting so intense that it could tune itself into an image as graphic as seeing, the evidence clearly shows that ultrasonic sonar accomplishes exactly that. And the bats, porpoises and other animals that use it discriminate between their own echoes and those of their companions, even where the frequency of the pulses is the same. This is hard to explain, but ultrasonic researchers reason that as the time dimension replaces some of the spatial dimensions when hearing replaces seeing, the creatures involved must begin to perceive both the amplitude and phase of the sound waves, discriminating among them in reference to a coherent background of ultrasound - which would mean that they have evolved a natural but unique bioholographic technique. This hypothesis in fact was tested in 1968 by Paul Greguss of the RSRI Ultrasonic Laboratory in Budapest when he made a model of a bat's brain which, operating at a frequency of one megacycle, produced actual ultrasonic holograms that could be recorded on soundsensitive photographic plates, scanned with a microdensitometer and used to reconstruct three-dimensional images of objects "heard" by the "bat".
Although the ultrasonic voices of bats vary from jet engine intensity (in the swift ones) to a dainty whisper (in the hovering ones), some of the moths and smaller insects they prey on can hear them from more than a hundred feet away and take effective evasive action, sometimes diving to the ground where they may be completely out of sonar
range. But, more amazing, is the fact that certain advanced moths not only dodge the bats but emit countersonar ultrasonic signals to confuse them when they get close. In one test, made with a high-speed movie camera synchronized with an ultrasonic tape recorder for playing back as audible slow motion, 85 percent of the bats hunting such moths actually abandoned the chase in the critical last second. And, as if jamming bat sonar weren't enough, parasitic mites have also been discovered living on the same moths, where they have quietly evolved a curious appetite for the soft flesh of one ear - only one ear, mind you, not both, because all the greedier mites that partook of the second ear have thereby long since doomed their breed into extinction by becoming suicidal passengers on a deaf moth who, through this very act, turned into easy bat fodder.
PRESSURE SENSE
Although the pressure sense takes many forms, from warning a bird of a storm to informing a mole of a predator, the, most observable of the various pressure organs is probably the fish's lateral line system that extends from his head along each side of his body to his tail. In many fish it is a clearly visible narrow dark line with thousands of sensilla (sense receptor cells) and their nerve connections that apprise the animal of low-frequency vibrations and pressure waves, coming through the water from anything solid nearby. Neurologists say it is a sense midway between hearing and touch, difficult to comprehend yet vital to the fish in locating prey, warning of enemies and enabling a school of fish to maneuver as a perfectly coordinated superorganism.
SENSES OF TOUCH
Here we come to other senses of feeling that are more commonly understood as such or, more specifically, as senses of touch. For a little reflection will tell anyone that there are some half dozen different tactile sensations that not only have different conscious aspects but distinct sets of specialized nerves to convey their messages to the brain. When you touch something, for instance, you generally become aware not only of its size, shape and texture, of its hardness or softness and its roughness or smoothness, but also of its temperature (through molecular movement or radiation, as we have seen), its humidity and perhaps its weight, pressure or motion, on occasion including a degree of painfulness, itchiness, ticklishness, sexiness, etc., not to mention a possible clue as to its nature, needs, potentialities or intentions. And the relative importance of the sense of touch may be hinted at by the known fact that a blind cricket enjoys a normal status among his fellows while a cricket with his feelers missing is lucky to survive a day.
Because there has been so little serious research in the field of touch, I offer you a relatively frivolous experiment into its variegated facets that were dramatized in 1969 when a kind of "feel museum" was opened to the public at California State College. According to reports, the visitors groped in silent smell-less darkness through rubbery channels, oscillating fur muffs, swinging rods, erotic pillows, stone walls, bags of lukewarm liquid and scores of other sensations deemed needed by a touch-starved civilization. Reactions to this socalled Tactile Symposium ranged from "fearful" to "sexy." One young lady who had resurfaced in the buff, dress in one hand, brassiere in the other, murmured, "It's too much of an experience. I didn't understand why I was wearing these clothes." Another sighed, "It's like taking your bed to bed."
The nerves that feel shape and texture would seem to be more delicate than most of us realize, because tests reveal that the average person can detect an eminence on etched glass no higher than one twenty-five-thousandth of an inch, especially if a thin piece of paper is placed between fingers and glass and moved with the fingers to unmask the friction of direct contact. A barefoot housewife may have cleaner floors because she can better feel the dust than see it. And to someone deprived of other senses, touch alone can be exalting. Helen Keller, then still a girl, wrote in her diary: "I have just touched my dog. He was rolling on the grass with pleasure in every muscle and limb. I wanted to catch a picture of him in my fingers, and I touched him lightly as I would cobwebs. But to, his body revolved, stiffened and solidified into an upright position, and his tongue gave my hand a lick. He pressed close to me as if he were fain to crowd himself into my hand. He loved it with his tail, with his paw, with his tongue. If he could speak, I believe he would say with me that paradise is attained by touch."
The main other locale of feeling is inside the body where our socalled proprioceptive or "muscle sense" keeps us i
nformed (mostly subconsciously) of important bodily functions and especially of our Posture, such as the precise positions of our limbs and fingers when they are in rapid coordinated motion.
SENSE OF WEIGHT AND BALANCE
A different sort of discernment tells us where we are in relation to the force of gravity. A simple way to test it is by weight judging, which has shown that the average person can barely perceive the contrast between two objects whose weights differ by two percent. As to balance, it is known that we sense it by a loose, round, pebblelike bone called the otolith in the inner ear which, like the primitive statolith (page 203), continuously rolls to the bottom of a tiny cavity, touching hairs that tell us which way we are leaning and how to walk straight. The vegetable version of the same sense is called geotropism and works through hormones (page 61). Flies, on the other hand, keep balance in flight by means of vibrating rods known as halteres. And fish use buoyant internal bladders containing gas.
SENSE OF SPACE AND PROXIMITY
The special awareness that enables animals to keep the same distance apart when moving in formation, and to know how near they may let a stranger or an enemy approach, is less well understood. But it works unfailingly and zoologists presume it is augmented by such other senses as sight, hearing, smell, sonar and the fish's lateral line.
CORIOLIS SENSE
This is probably the least known among feeling senses if indeed it is properly so classified. For exactly what kind of inertial perception, if any, makes it possible for a migrating fish or bird to feel the turning of Earth remains unestablished. However the Foucault pendulum, which reveals earthly rotation by the relative change in its plane of swinging, is a manmade Coriolis instrument that could have an analogue in life.
This chapter has dealt mainly with the eyes and ears of the world. But it is time we moved on to Earth's more numerous and often less known senses, which involve invisible, silent molecules and the intangibilities of the psyche. These are hardly less important than sight and hearing, for all the senses yet discovered are part of the living Earth - indeed the very means by which she has begun to know herself and will soon know much more.
Chapter 8
Twenty-one Senses of Chemistry, Mind and Spirit
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SO WE ARRIVE at what are often called the visceral or chemical senses, meaning those that enunciate the appetites for food, drink and, in some cases, physical love. And right off we encounter smell and taste, which work chemically and are thought to be the most experienced of all senses. If this is true, it is presumably because chemistry deals primarily with molecules, which are the material units composing the world, including all its organisms, and which therefore interact with creatures directly rather than indirectly through waves of radiation or compression, as in the cases of vision and hearing. Thus when organized life evolved on Earth several billion years ago, the first way it could sense anything almost inevitably had to be through direct contact, naturally at the molecular level, as earthly life had not yet organized larger units except such structures as crystals which, if they are definable as alive, may also be regarded as molecules or more accurately, supermolecules.
So did smell and taste (originally one sense) come into our world. At first the smell-taste organ (if it could be considered such) must have occupied practically the whole body, making the viruslike creature in effect a living nose or tongue. Then, as macroscopic life appeared, the organ retained its central forward position at the business end of its owner, while the snout took shape and, doing so, started to create the face.
SMELL
Life must have tried out a lot of questionable smellers during those primordial and invertebrate eons if we are to judge by the olfactory organs now to be found in the mycelia of fungi, in the palps of insects, on the heads of worms, in the feet of ticks, in the gills of mollusks.
But by the time the backbone established itself as the prime feature of progressive earthly bodies, the nose had become more or less standard in its present dominant position in fish, reptiles, birds and mammals.
This is not to say that these animal classes are anywhere near equal in their sensitivity to smell. For birds are primarily creatures of vision, secondarily of hearing and, with the exception of ducks, petrels, shearwaters and albatrosses, relatively insensitive to smell. This, incidentally, may be advantageous to the great horned owl, he having excellent night vision as well as sonar to help him prey on nocturnal animals such as the skunk, because the skunk's fragrance is well known to repel practically everyone else and undoubtedly would repel the owl too if he were not so smuff. The word "smuff," I should explain, is the adjective I use instead of the sterile medical term "anosmic" to describe one lacking a sense of smell. I forged it out of "snuff" + "muff" because obviously smell-less creatures need an apt one-syllable word corresponding to blind and deaf, since, after all, the world contains not only those who are stone blind and stone deaf but, less conspicuously, an estimated two percent who are stone smuff!
If smuffness is prevalent among mercurial, clear-eyed creatures like birds, however, it is a lot rarer among the relatively plodding fish, almost all of whom are able to find their food, if not their way home, quicker through their nostrils than through their eyes. I'm thinking of the shark who smells blood two miles away and of the salmon who remembers the individual flavor of the brook he was spawned in from among hundreds of tributaries of a great river.
Reptiles, notably lizards and snakes, use their sense of smell pretty constantly, but augment it with a supplementary sense that seems to combine smell and taste in the manipulation of their forked tongue,
which, as nearly everyone knows, they flick in and out at frequent intervals. What the forked tongue does is pick up molecules by the million, mostly out of the air, pulling them into the mouth and smearing thousands of them over two holes in the roof of the mouth which are entrances to a chemoreceptor known as Jacobson's organ, that instantly smell-tastes them. This is how a rattlesnake, for example, locates a rabbit he has bitten but which afterward scampers off in a panic for hundreds of feet before collapsing. The same technique helps reptiles find mates and to congregate when the season arrives for hibernation.
It is the mammals, however, warm-blooded and intricately social, who have developed the sense of smell the most of all, demarking their territories with odor fences and migrating long distances by smell navigation. A debate has been going on for centuries, for example, about how dogs that have been taken by strangers in closed vehicles to some strange town often manage to find their way home alone through a hundred miles of unfamiliar country. Alfred Russel Wallace theorized that such animals must automatically remember a "train of smells" when- or wherever they go and that they later somehow rerun the "train" in reverse, perhaps including many sidetrack trials and errors. Whatever truth there may be in the concept, however, hardly explains the dog's observed ability to take major shortcuts without getting lost, or his diverging sometimes scores of miles away from anywhere he had ever been. Could smell possibly carry that far? I wonder.
Even though odors can be wafted great distances on the wind and the keenest scented animals have proven they can detect a test aroma diluted to 10 -13 or only one molecule in ten trillion of average air, it still is hard to believe the confirmed reports that bloodhounds and other trained dogs have found a lost wallet, a gun or a vial of heroin under tons of manure, or concealed in a chemical factory reeking with fumes of sulfur or ammonia. The explanation seems to be that no smell can completely cancel or camouflage another smell because the molecules both smells consist of are irretrievably diffused throughout the air they are in, and any two or more simultaneous odors, no matter how mixed, are smelled alternately in the olfactory cells and nerves, even though the alternations may be only milliseconds apart. Furthermore a dog who has sniffed, say, a man's cap can later recognize any other part of him and easily follow his trail because there are recognizable olfactory relationships between body parts as well as between species, races,
sexes, ages, diets, diseases, neighborhoods, occupations or almost any other classifications of life.
If you want to avoid being tracked by a dog, then the first thing to do is wear brand-new shoes or cover your old ones with untouched plastic bags, so that the fewest possible molecules from your feet are left on the ground. But, in an actual case, even if no telltale molecules from your body get left behind (something manifestly impossible) an experienced dog may be able to follow you by smelling the freshly crushed grass or disturbed soil where you stepped, for this is the dog's specialty: he carries his nose close to the ground and the smelling part of his brain is not only disproportionately large but specialized to detect tiny traces of substances such as aliphatic acids in sweat that seep through shoes and diffuse steadily outward in air. In fact smell to him is a little like sound to a bat, giving him a degree of what we seeing-creatures call visualization. This was nicely demonstrated by a researcher who blindfolded a hound at a rabbit show and noted the "olfactory nystagmus" produced when a passing parade of rabbits caused the dog to swing his head back and forth as he smelled each in turn, something like an onlooker at a tennis match or a child scanning a book. Indeed one might reasonably have described the hound as "reading" rabbits with his nose.
Animals are usually more widely separated than this in their natural state, however, so it may be worth mentioning that auras of both sound and smell outdoors normally take ellipsoidal forms, extending mostly downwind from the animal or plant originating them. This is particularly true of smell whose dome-shaped diffusion is of course part of the total organism, its volume generally inversely proportional to the wind velocity, though a strong wind may waft a few thin odor streamers for great distances.
