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Why and How do Cats Purr?
Ever since the Egyptians started worshipping the cat, philosophers, scientists and cat lovers worldwide have wondered why cats purr.
— unknown
Surfing around the net, I've compiled some explanations. You can read their here. I'm very interested in this theme. If you have some other things to this topic to contribute, please feel free to mail me.
longword@newsguy.com (Lionel Lauer) wrote:
Kibo informs me that joez@earthlink.net (Joe Zeff) stated that:
jfb@www.wavefront.com () wrote:
Otto does this with me by choosing the most hung-over/lonely mornings to curl up in my knee pit, purring like a 6hp briggs & stratton.
All cats purr at 28hz.
I think your cats need tuning — according to a couple of quick measurements on a recently calibrated reference cat, the dominant frequency of a correctly adjusted cat should be 12Hz +/-20%.
I have a book on cats at home that claims this. I can get the reference if anybody really cares.
--
------------------------------------------------------------ Joe Zeff Earthlink Network joez@earthlink.net Senior Support Joat (800) 395-8410 Computers work in weird and marvelous ways, their wonders to avoid performing. ------------------------------------------------------------From: joez@earthlink.net (Joe Zeff), Subject: Re: My desk has been invaded..., Date: 1998/08/11, Message-ID: <35db9550.18983686@news.earthlink.net>, Approved: Liason for Altruistic Re-educational Therapy, Newsgroups: alt.sysadmin.recovery
Meow!
Domestic cats purr at about 26 cycles per second, the same frequency as an idling diesel engine. A domestic cat hears frequencies up to about 65 kHz, humans up to 20 kHz. Its sense of smell is about 14 times stronger than that of humans.
Q: Why do cats purr? —Amber
A: Well, Amber, the answer to your question is a mystery to me—and to the many scientists who have studied cats and cannot figure out exactly why they purr! If you have a kitty, you've probably heard that familiar rumble when you pet her or when she's sitting all content and cozy on your lap—there can be no doubt she's all-out happy! But cats also purr when they are really sick or really scared.
Some researchers say that perhaps they are trying to comfort themselves.
Why do cats purr?
J. Stone
Richmond, Va.Leslie A. Lyons, an assistant professor at the School of Veterinary Medicine at the University of California, Davis, explains.
Over the course of evolution, purring has probably offered some selective advantage to cats. Most felid species produce a "purr-like" vocalization. In domestic cats, purring is most noticeable when an animal is nursing her kittens or when humans provide social contact via petting, stroking or feeding.
Although we assume that a cat’s purr is an expression of pleasure or is a means of communication with its young, perhaps the reasons for purring can be deciphered from the more stressful moments in a cat’s life. Cats often purr while under duress, such as during a visit to the veterinarian or when recovering from injury. Thus, not all purring cats appear to be content or pleased with their current circumstances. This riddle has lead researchers to investigate how cats purr, which is also still under debate.
Scientists have demonstrated that cats produce the purr through intermittent signaling of the laryngeal and diaphragmatic muscles.
Cats purr during both inhalation and exhalation with a consistent pattern and frequency between 25 and 150 Hertz. Various investigators have shown that sound frequencies in this range can improve bone density and promote healing.This association between the frequencies of cats' purrs and improved healing of bones and muscles may provide help for some humans. Bone density loss and muscle atrophy is a serious concern for astronauts during extended periods at zero gravity. Their musculo-skeletal systems do not experience the normal stresses of physical activity, including routine standing or sitting, which requires strength for posture control.
Because cats have adapted to conserve energy via long periods of rest and sleep, it is possible that purring is a low energy mechanism that stimulates muscles and bones without a lot of energy. The durability of the cat has facilitated the notion that cats have "nine lives" and a common veterinary legend holds that cats are able to reassemble their bones when placed in the same room with all their parts. Purring may provide a basis for this feline mythology. The domestication and breeding of fancy cats occurred relatively recently compared to other pets and domesticated species, thus cats do not display as many muscle and bone abnormalities as their more strongly selected carnivore relative, the domestic dog. Perhaps cats' purring helps alleviate the dysplasia or osteoporotic conditions that are more common in their canid cousins. Although it is tempting to state that cats purr because they are happy, it is more plausible that cat purring is a means of communication and a potential source of self-healing.
Answer posted on January 27, 2003
The Remarkable Purr of a Cat
Why and How do Cats Purr?
My mailbox often brings interesting challenges, as in this morning's short question from Gideon: "Do cats purr when they are alone?" What a great question! As I replied to Gideon, it is on the order of, "If a tree falls in the woods, and there's no one there to hear it, does it make a sound?" Or - "Does the light burn inside a closed refrigerator?" Yet, by far, I think the question about cats purring is the much more fascinating of the three. Truthfully, I don't know if cats purr when they are alone. It seems likely that they do, if one understands a little about why cats purr.
Most experienced "cat wranglers" now know that cats don't purr only when they are content and happy. They also purr during tense or traumatic moments. When suddenly and violently injured, even at moments near death, a cat will often purr. I've often likened this to saying, "Please don't hurt me any more. I'll be good," but recent studies have put a more scientific spin on this seeming anomaly.
It seems that the measurable Hertz of a cat's purr lies between 25 and 150.
Coincidentally (or not) it has been found that sound frequency in this range can stimilate bone growth and healing. (SCIENTIFICAMERICAN.com: Why do cats purr?)That cats have remarkable endurance, and are quite stoic to trauma is well known to veterinary professionals; it is not unlikely that this instinct to purr under duress is directly related.
Purring under stress has more colorfully been described as the cat's mantra, e.g., a self-soothing, self-healing, relaxing, vibrating sound (sort of like the Ommmm one might hum while in the lotus position. Notice the vibration in your lips, nose and throat? I bet most of us, if we had our "druthers," would much rather be able to purr!
The Physiology of Purring
There seems to be two schools of thought here.
- The most popular one is quoted here:
One study determined that purring involves activation of nerves within the voice box. These nerve signals cause vibration of the vocal cords while the diaphragm serves as a piston pump, pushing air in and out of the vibrating cords, thus creating a musical hum.
Veterinarian Neils C. Pederson, author of Feline Husbandry, believes that purring is initiated from within the central nervous system and is a voluntary act. In other words, cats purr only when they want to. (PetPlace.com: Why Do Cats Purr?)- The other theory is that the sound comes more from vibrating blood vessels than in the voicebox itself. (Mad Science Network: How Does A Cat Purr, Which Cats Purr, and What Does It Mean?)
The Happy Purr of a Cat
All domestic cats are born with the purring ability. A queen will purr while giving birth. It is unknown whether this is because of happy anticipation, or whether it is a relaxing "mantra." Kittens instinctively purr when nursing, and the momcat purrs right back at them. Your adult cat will purr at the drop of a hat whenever you're near, and especially when you are holding or petting him.
Cat purrs will range from a deep rumble to a raspy, broken sound, to a high-pitched trill, depending on the physiology and/or the mood of a cat. A cat will often "wind-down" when going to sleep, with a long purring sigh that drops melodically from a high to a low pitch. Does your cat's purr sometimes sound like an idling diesel engine? That's because at the lower range of 26 Hertz, the velocities are nearly the same.
The Healing Power of the Purr
Cats are often used as "therapy animals" in convalescent hospitals, or in retirement residences. It is an accepted fact that cat owners have lower blood pressure, especially in older people. The human- feline bond is never quite so close as when a person is holding and petting a purring, vibrating bundle of fur on her lap, and all is well with the world. You may even find yourself purring in response.
~ Franny Syufy
Why and how do cats purr?
Purring is part of every cat's repertoire of social communication, apparently created by the movement of air in spasms through contractions of the diaphragm. Interestingly, purring is sometimes heard in cats who are severely ill or anxious, perhaps as a self-comforting vocalization. But, more typically, it is a sign of contentment, first heard in kittens as they suckle milk from their mother.
In adults, purring is heard in domesticated cats when they are petted, and in feral cats during sexual or other social contexts.
Like submissive posturing among dogs, purring may be a signal of appeasement to other cats or to people, a way to communicate that the purring cat need not be threatened.As with many behaviors in dogs and cats, the original presumed purpose of the behavior may not be directly relevant in a pet home.
But we do believe that, when our healthy pet cats purr, they are happy and at peace.
An accelerometer was also used to measure domestic cat purrs. Every felid in the study generated strong frequencies between 25 and 150 Hz. Purr frequencies correspond to vibrational/electrical frequencies used in treatment for bone growth/fractures, pain, edema, muscle growth/strain, joint flexibility, dyspnea, and wounds. Domestic cats, servals, ocelots, and pumas produce fundamental, dominant, or strong frequencies at exactly 25 Hz and 50 Hz, the two low frequencies that best promote bone growth/fracture healing [Chen et al., Zhong. Wai Ke Za Zhi. 32, 217--219 (1994)].
Results indicated that despite size and different genetics, all of the individual cats have strong purr frequencies that fall within the range of a multitude of therapeutic frequencies and particular decibel levels, see Fig. 3. Frequencies of 25 and 50 Hz are the best, and 100 Hz and 200 Hz the second best frequencies for promoting bone strength. Exposure to these signals elevates bone strength by approximately 30%, and increases the speed at which the fractures heal.
Purring the Pain Away
All the cats had purr frequencies between 20 Hz and 200 Hz. With the exception of the cheetah, which had frequencies ± 2 Hz from the rest, all the species had frequencies, notably 25 Hz, 50 Hz, 100 Hz, 125 Hz, and 150 Hz, that correspond exactly with the best frequencies determined by the most recent research for bone growth, fracture healing, pain relief, relief of breathlessness, and inflammation. All of the cats' purrs, including the cheetah, had frequencies ± 4 Hz from the entire repertoire of low frequencies known to be therapeutic for all of the ailments.
According to Cat World: A Feline Encyclopedia by Desmond Morris (Penquin Reference, 1997), there are two theories as to how a cat purrs:
"The False Vocal Cord Theory: This sees purring originating in the cat's voicebox, or larynx. In addition to the ordinary vocal cords, the cat possess a second pair of structures called vestibular folds, or false vocal cords. The presence of the second pair is thought to be the secret behind the extraordinary purring mechanism that permits the animal to produce the soft, rumbling sound for minutes and even hours on end without any effort..."
"The Turbulent Blood Theory: this says that the cat's voice box has nothing whatever to do with purring. Instead, it is argued that when the cat's blood-flow through its main veins into the heart in increased, turbulence in created. This is greatest at the point where the main vein... is constricted as it passes through the animal's chest. The swirling blood is thought to make the purring noise, the diaphragm acting as an amplifier of the vibrations. The noise thus created is thought o be passed up the animal's windpipe and into the sinus cavities of the skull where it resonates to produce the purring sound..."
I prefer to leave it a mystery, myself
Gabrielle
From: Gabrielle or Hop David <cunews@tabletoptelephone.com>, Subject: Re: Cat's Purr, Date: 1998/01/05, Message-ID: <34B188C5.512B35D1@tabletoptelephone.com>, Reply-To: cunews@tabletoptelephone.com, Organization: Ajo Copper News, Newsgroups: rec.pets.cats.health+behav
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