Text: http://www.telegraph.co.uk/et?ac=004582369062218&rtmo=fsw0rlMs&atmo=rrrrrrrq&pg=/et/01/3/18/wcat18.html SCIENTISTS have discovered that the purring of cats is a "natural healing mechanism" that has helped inspire the myth that they have nine lives. None lives: wounded cats purr because it helps their bones and organs to heal. Wounded cats - wild and domestic - purr because it helps their bones and organs to heal and grow stronger, say researchers who have analysed the purring of different feline species. This, they say, explains why cats survive falls from high buildings and why they are said to have "nine lives". Exposure to similar sound frequencies is known to improve bone density in humans. The scientists, from the Fauna Communications Research Institute in North Carolina, found that between 27 and 44 hertz (a measure of the number of cycles per second) was the dominant frequency for a house cat, and 20-50Hz for the puma, ocelot, serval, cheetah and caracal. This reinforces studies confirming that exposure to frequencies of 20-50Hz strengthens human bones and helps them to grow. Dr Elizabeth von Muggenthaler, the president of the institute, said: "Old wives' tales usually have a grain of truth behind them and cats do heal very quickly. The healing power of purring seems to explain their 'nine lives'." The scientists say that sound waves created at a particular frequency trigger the healing process in feline bones. Purring is believed to have a similar effect to ultrasound treatment on humans. Dr von Muggenthaler said: "We are starting to solve a 3,000-year-old mystery as to why cats purr. The next phase will be to explain the mechanics of the process." Almost all cats purr, including lions and cheetahs, though not tigers. Dr. von Muggenthaler said that purring had to be advantageous to a cat to survive natural selection, but there seemed to be no obvious advantage for a cat merely to display contentment. A natural capacity for increasing bone growth and strength and reducing healing time was, however, "clearly advantageous". Cats' ability to survive and recover quickly after falling from tall buildings is well documented. One recent study, published in The Journal of the American Veterinary Medical Association, found that out of 132 cats that fell an average of 5.5 storeys, 90 per cent survived, including one that fell 45 storeys. Other scientific teams are researching whether "sound treatment" could be used to halt osteoporosis and even renew bone growth in post-menopausal women. Dr David Purdie, from Hull University's centre for metabolic bone disease, said that the human skeleton needs stimulation or it begins to leak calcium and weaken. "Purring could be the cat's way of providing that stimulation for its own bones." He said that it was difficult to devise physical exercises for old people suffering from osteoporosis and speculated that it might be possible to create a mechanism to use cats' purring to help strengthen elderly bones.

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