**Notice to readers. The following is layman's version of a speculative research paper. It is a hypothesis. The definition of hypothesis is "a tentative suggestion" and science would not occur without them. Since we have only just begun this study, and as yet nothing has been proven  (except for referenced research and the frequency range of the cat's purrs), this paper is not designed to give veterinary or medical advice.** 

All smaller felids, including the domestic cat, caracal, serval, puma, ocelot, and even some large cats such as lions and cheetah purr. Since the 1970's no one has pursued research into the 3000-year-old question, "Why do cats purr?" Perhaps it is because, one, we didn't have the knowledge we have now, and two, it was simply easier to assume that cats purr when they are content, which cannot be argued-they do purr when they are content. The contentment hypothesis, however, clearly cannot be the only reason cats purr:

 (1) A vocalization is used to display a particular emotion or physiological state. This enables an individual in society or pack to be able to express themselves.  As any cat owner knows well, there are different "meows" for different emotions. A cat owner knows the difference between their cat's  "fearful hiss" and  "food meow". This cannot be applied to the purr however. Cats purr even when they give birth and when severely injured in a barren cage at the veterinarian's. There are cases of cats purring when they are in grave physiological or psychological stress, as well as when they sit on your lap. Therefore, purring really cannot be considered a vocalization, as the purr is produced under differing emotions or physiological states. As an example, a cat hissing when he/she was happy and when he/she was scared, would confuse the rest of the cat's companions and probably would lead to him/her being ostracized. 

(2) Natural selection insures that a particular trait be advantageous to an animal. Admittedly, there is some benefit to be obtained from purring to one's self or to kittens, (a sort of kitty lullaby if you wish).  Yet, there does not appear to be a strong 'survival' advantage to this behaviour, unless, of course, you wish to constantly display submission.  For the purr to exist in different cat species over time, there would likely have to be something very important (survival mechanism) about the purr. There is also a very good reason for energy expenditure (in this case creation of the purr), when one is physically stressed or ill. It would have to be somehow involved in their survival. 

  Old wives' tales usually have a grain of truth behind them, and most people have heard of a cat's "nine lives." There is also an old veterinary adage still repeated in veterinary schools which states, "If you put a cat and a bunch of broken bones in the same room, the bones will heal."  Any veterinary orthopaedic surgeon will tell you how relatively easy it is to mend broken cat bones compared with dog bones which take much more effort to fix, and  take longer to heal. There is excellent documentation of the cats' quick recovery from such things as high-rise syndrome.  First mentioned by Dr. Gordon Robinson in 1976, high-rise syndrome was later studied by Whitney, W., and Mehlhaff, C., (1987) the Journal of the American Veterinary Medical Association. They documented 132 cases of cats plummeting many stories from high-rise apartments, (average 5.5 stories) some suffering severe injuries. Interestingly, 90% of these cats survived. The record for survival from heights is 45 stories, however most cats suffer from falls of 7 stories or more and manage to live.

  There has been some research that suggests that domestic cats are in general less prone to postoperative complications following elective surgeries. Using computer records, Pollari and Bennet, (1996) state that complications following surgery for dogs undergoing castration to be averaged at 9.8%. The same surgery for cats lists the rate of complications to be 1.2%. Dogs undergoing overiohysterectomies (OHE) had complications 17.4% of the time and cats 8.4%. In another study by the same authors comparing paper records with computerized documentation, dogs undergoing castration complications varied from 2.4% to 22%, in cats 0.0% to 6.3%. With OHE complications varied from 6.5% to 17.7% in dogs and 3.6% to 16% in cats. Lund et al. (1999) the records of 31,484 dogs and 15,226 cats at 52 veterinary practices to determine the most common disorders. Arthritis in dogs was listed as 2.4% of the population and was not listed as being reported in the cat. The prevalence of lameness in dogs occurred 3.1% of the time, in cats it is not mentioned as being reported. Healthy dogs were listed as 6.8% of the dog population, healthy cats 9.5%.

Bone and muscles/ligaments

  Although it is impossible to standardize the healing time for dogs and cats in clinically occurring fractures, due to the type of fracture, amount of trauma to soft tissues, the type of treatment, the standard evaluation time or the after care, some general statements can be made, (Johnson, 2001). Cats do not have near the prevalence of orthopaedic disease or ligament and muscle traumas as dogs do. Additionally, Toombs et al. (1985) suggests that non-union of fractures in cats is rare.

  Osteo diseases that are rarely found in cats but can be found in all breeds and sexes of dogs include; Osteochondritis dissecans of the proximal humerous, scapulohumeral joint luxations, hip dysplasia. Osteo diseases in which cats are completely unaffected include fragmented coronoid process, ununited anconeal preoceese, traumatic elbow luxation, elbow subluxation, and legg-perenes. Osteosarcoma occurs much less frequently in the cat then in the dog. Johnson, 1999. Osteoarthritis and CPPd have only been found in large cats that were raised in zoological parks. The frequency of effected cats in the wild is apparently so low, that they are infrequently affected by these diseases in the wild. (Rothschild et al., 1998)

  Myeloma is a tumor of plasma cells originating in the bone marrow. Only eight cats with multiple myeloma have been reported to have osteolytic bone lesions. 56% of all dogs reported with this condition involve bone. The metastatic behavioural differences between dogs and cats is that tumours in the dog involve the whole body, whereas in the cat it involves the distal ends of the extremities. In Lameness

  With regard to the prevalence of ligament and muscle injuries and disease, those that are seen regularly in dogs but not in cats include, cranial crutiate ligament ruptures, meniscal injuries (torn ligaments), muscle contusions and strains, muscle contracture and fibrose, quadriceps contractor and inialsinatus, bicipital tenosynovitis, medial patellar luxation, lateral patellar luxation, osteochronditis dissecans of the stifle, and ligamentous injury of the tarsus. (Johnson)

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One Cat is Company

"One cat is company.
Two cats are a conspiracy. 
Three cats is an attempted takeover.
Four or more cats is a complete coup!"

Shona Steele (Australia)

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