The Magical, Mysterious Purr

Once upon a time a comely princess faced a seemingly impossible task. To save her true love from death, she had to spin 10,000 skeins of linen in only 30 days. Heartbroken, the princess wept in frustration until her three cats took pity on her and agreed to help. With their rough tongues and swift, clever paws, the cats not only finished in plenty of time, but the linen they spun was the finest and most wondrous ever seen in the kingdom. The cats' reward? They were blessed with the ability to purr, so they and their descendants would forever be living manifestations of the mesmerizing whir of the spinning wheel. The purr is more than a feline vocalization, more than a physiological oddity. Even among the cat's remarkable collection of unique attributes, the purr stands alone. It is singular, personal, distinctive true feline performance art. The mysterious, uncannily soothing vibration, sometimes felt but not heard, other times rafter rattling, is at once eminently practical and one of nature's glorious luxuries. A cat purrs to soothe and flatter its human companions; to celebrate and reinforce the familial bond among its own kind; to lull its kittens to sleep or call them to dinner; to reveal its emotional state; to manipulate and cajole; to entreat; to acknowledge friendship or approval; to revel in joy, thanks and contentment; to please its ineffable self. As both quintessentially feline self- expression and an admirably versatile communicative device, the purr is unequaled. Yet the purr remains a mystery. For some experts, this produces a peculiar avoidance: Some books devoted to feline nature and behavior fail to even mention the purr. The cat, whose bond with humanity is both ancient and extraordinarily intimate, seems determined to keep some of its secrets tucked away - probably right behind its purr box. In Paul Gallico's wise classic The Silent Miaow, the narrator cat unequivocally and proudly claims, "No one has ever been able to discover how we make this subtle sound, and what is more, no one ever will. It is a secret that has endured from the very beginning of the time of cats and will never be revealed."
Cords to Boxes
No one is entirely sure how a cat purrs. An obvious problem is that by the time an investigator gets in to search out the mechanism, the cat has stopped purring. Science offers three principal theories, none universally accepted. In addition to their vocal cords - structures that enable them to produce all the yowls meows, growls and squeaks that form their extensive vocabularies cats possess another set of structures called vestibular folds, often referred to as false vocal cords. When air is inhaled and exhaled, the false vocal cord theory postulates, one of the folds rubs against the other, producing the vibrating purr. This theory seems to be steadily losing ground. Proponents of the muscle contraction theory believe that some of the cat's laryngeal muscles contract, causing a buildup of pressure and resulting vibrations. A more compelling theory is the turbulent blood flow model, which proposes that purring is hemodynamic rather than aerodynamic in origin. The palpable purring vibration originates in a large vein, the vena cava, in the cat's thorax, or chest cavity. Where the vena cava passes through the diaphragm, the contraction of the muscles around the vein constricts the blood flow, causing a transition from a smooth flow to a turbulent one. This sets up oscillations, similar to the motion seen in a fluttering flag. The vibrations are then transmitted and amplified through the air-filled bronchial tubes and the trachea (windpipe) to the sinus cavities of the head. Powerful support for this theory comes from the case of a Manx cat that had been injured by a dog. Its diaphragm was ruptured and its trachea severed. Yet, rendered voiceless by its injuries and by the medical procedures required to save its life, the cat still purred. There was no sound from the throat, but the vibrations were easily detectable in the cat's chest. In other observations of injured cats where the injuries rendered the heart and chest sounds clearly distinguishable from the purring vibrations, the rhythm of the purrs could be synchronized neither with breathing nor with heart sounds, indicating an independent mechanism. The turbulent blood theory also holds that when a cat's back is fully arched, blood velocity is maximized, and therefore, purring is strongest. Indeed, as your happy cat arches its back to your stroking hand, its purring soars to new heights of intensity and volume. Similarly, a furious cat, arching its back to face an imminent threat, produces a highly tuned vibration that can be easily felt but is seldom audible. Those bewildered by competing scientific theories might appreciate B. Kliban's brilliantly simple proposition. In a memorable drawing in his sagely amusing book Cat, the prolific cat cartoonist offers a typically quizzical Kliban cat upon whose throat has been traced, in dotted lines, a small box. In the enlarged view of that mysterious device, Kliban has sketched wires, connectors and other vaguely mechanical-looking hardware. On the front is a dial tunable from soft to loud. Logical, elegant, flawless. The drawing's title? "Purr Box," of course.

Emotion Over flow

Whatever the physical mechanism, a cat's purr prowess is symbolic of its intrinsic capacity for self-expression and its desire to communicate, if only with itself. We talk to ourselves. Why shouldn't a cat? Many observers believe that a cat's purr indicates an overflow of emotion, a true measure of profundity. A cat overflowing with any intense emotion-contentment, joy, fury, pain, fear-purrs. Caregivers are sometimes shocked to hear a deep purr resonating from a badly injured or dying cat. Perhaps the rhythmic vibration of the purr is as comforting to the cat as it is to its human companions. Researchers have demonstrated that stroking a purring cat can lower human blood pressure and pulse rate, as well as increase feelings of peace and well-being. Anyone who lives with a cat will attest to the calming, even hypnotic effect of a purring, kneading cat. One woman, who with her imperturbable cat has endured thousands of aftershocks since the January 1994 earthquake in the San Fernando Valley near Los Angeles, is a passionate believer in purr therapy. "I've learned so much from my cat these last few months," she says. "Tabby hates the aftershocks as much as I do, but she stays close by. She seems to know how much I need her when I'm especially rattled. Soon after the shaking stops, she's on my lap, purring me (and maybe herself) back to sanity." Randy Moravec, in his delightful book Claude, attributes early humans' domestication of the cat directly to the purr. His tongue-in- cheek account illuminates an essential truth. "The cat didn't do much, was poor eating and preferred to hunt alone. On the other hand, it was soft, furry and emitted a pleasing purr, so the cat was tolerated for its aesthetic value and became the lava lamp of its day." In the interest of science, Moravec contributes the following statistic, based on his observations of Claude, "an underachieving indoor cat": "Total time a cat spends purring during its life: 10,950.13 hours.

Cat Communication

Does a purr mean anything, and if so, what? Such questions are addressed by the science of zoosemiotics, the study of communication between animals and the creatures with whom they interact. Zoosemioticians study the form, content and context of animal communications, tracking clues to motivation and intent. No cat caregiver can deny that purring is often a purposeful, goal-oriented, even manipulative activity The shrewd teacher cat in The Silent Miaow tells feline novices how it's done. She divides purrs into two classes: the Post-Appreciative or Thankful Purr and the Anticipatory Purr. Both are ideal for manipulating vain humans, she asserts. The first will "engage the vanity and aggrandize the donor of whatever it is that has caused your manifestation of satisfaction." The second is a "powerful stimulant if you want some action." But the most effective purr, suggests the perceptive instructor, is the Withheld Purr - highly effective if your people have transgressed and you are engaged in letting them know that they have and punishing them." Among cat-kind, purring serves a variety of communicative functions.
A cat about to give birth accompanies her labor with continuous, powerful, rhythmic purrs. As each kitten is born tiny, helpless, blind and without much hearing or sense of smell-Mama's reassuring vibration serves as a homing beacon to help the little one find its place on the chow line. Perhaps the purr soothes and calms Mom as well, aiding her concentration, keeping her mind off her own discomfort and providing a reassuringly familiar sonic shield against the stress of kittening. When the kittens are about 2 days old, they spontaneously begin to purr as they suckle. The delicate vibrations help the tiny kits orient themselves and serve as a signal to Mom that milk is flowing and all is well, much like the smile of a baby. As the kittens mature, they are often called to dinner by one of their siblings, who latches onto a familiar nipple and commences the startlingly loud and forceful "dinner gong" purr. All this communal purring helps create and maintain a close, warm family relationship especially important in the little ones' first weeks of life, when their reliance on Mom's protection is absolute. In adult cats, purring is sometimes used as a signal of appeasement by a subordinate cat toward a dominant one. Here, purring likely reduces the chances of an attack or fight, distracting the aggressor or awakening in its mind peaceful and conciliatory images of kittenhood. A female cat purrs almost continuously during courtship and mating. Again, this probably helps reduce stress in an often tense and quite possibly dangerous situation. Individual cats vary widely in intensity and frequency of purring, as well as in the particular situations that motivate them to purr. Some cats are enthusiastic, lively and habitual purrers; some just hum away quietly and decorously; some flaunt raspy, raucous (though no less charming) purrs or highly idiosyncratic purrs punctuated by chirps, whistles, wheezes or buzzes; others are so discreet that their purrs can be detected only by caressing their throats, feeling rather than hearing the velvety vibrations.

Musical Metaphors

The rich mystery and sensuality of the feline purr have long captivated poets and authors. In striving to convey the essence of this peerless feline phenomenon, writers often summon musical metaphors. One of Carl Van Vechten's cats purred "like the kettle drums in Berlioz's Requiem." May Sarton's delightful The Fur Person fairly hums and trills with the melodies of the purr. The purring repertoire of Tom Jones, Sarton's tiger cat, includes "just a tremolo," "a light elegant obbligato and "bass drums very lightly drummed." Randy Moravec, the chronicler of underachieving Claude, tells us, "A cat purrs at a rate of about 60 cycles per second. This is comparable to the typical rate of a 'Million Fingers' bed massage, and it seems that both have similar effects on people." Many others also swear by purr therapy, happily asserting that it's cheaper than tranquilizer and refreshingly free of side effects (except possibly those occasional purr-induced catnaps). Purring is unquestionably a force for good in the world. Author and animal expert Roger A. Caras muses upon the possible benefits of human purring ability. "Purring people would have to feel good about themselves and each other. Imagine how you would feel if you bumped into someone in an elevator and they purred instead of glared at you. And instead of muttering a self-conscious 'Excuse me,' you could purr back." An ancient saying holds that "To please himself only a cat purrs." Perhaps. Whatever the purring cat's private motivation, the ineffable pleasures of the purr radiate outward with that curiously soothing vibration-like ripples in a still pond-to resonate within the hearts of both human and feline beneficiaries. Our cats spin enchantment rather than linen; through the enigmatic purr, the cat's pleasure becomes our own.

This article was written by Wendy Christensen and appeared in CAT FANCY in 1994. Wendy Christensen, a contributing editor to CAT FANCY, shares her home with six champion purrers: Petunia, Dagny, Dominique, Bunny, Dandelion and Lady GreyShadows.

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