The Origin of the Purr

The purring of cats has long been one of the most interesting and controversial sounds in the animal kingdom. This phenomenon, not really understood until recently, has almost become folklore.

Several theories for the origin of the purr have been offered. At first, the larynx was considered the source. However, results of early experiments virtually dispelled this theory. When air was allowed to bypass the larynx in some cats, they could still purr.

Next, the sound was attributed to vascular sources. Researchers observed that cats most often purred while being petted and that they also tended to arch the back during that time. The theory went something like this: the arching of the back bent the aorta, the blood eddied at the sharp bend, resulting in turbulence that was heard as a purr. Investigators went so far as to induce local anesthesia at the site of an abdominal incision so they could manually palpate the aorta.

Not until recently has the mechanism for purring been found. Results of electromyographic studies of laryngeal muscles revealed regular stereotyped patterns associated with purring. As certain of these muscles contract, the glottis closes partially, causing a buildup of pressure caudal to or within the glottis. The turbulence of the air passing through the narrowed opening produces the purr. This explanation holds for purring that occurs when the cat is in positions other than the arched-back.

Meaning of the purr

Not all purring is associated with an audible sound. Cats often purr in the presence of their kittens or people. Despite the fact we can never truly know why cats purr, it is fun to speculate on the reasons. Some have said that a purr is somewhat comparable to our smile. The behavior occurs most commonly when cats seen to be happy, content or relaxed.

The most unusual occasion for purring is one most often seen by veterinarians. The chronically ill cat may purr during the late stages of illness right before death.

The conclusion is that the purr originates at the source of most vocalizations, the larynx. It probably communicates a feeling of contentment. It is interesting that is has taken scientists this long to figure out what most of us always thought it meant.

If you have questions contact Dr. Underwood of the Trumann Animal Clinic at catdoc56@pcsii.com.