13th Sense?

Everybody knows that man has five senses. But everybody is dead wrong, according to an article in the A.M.A. publication, Today's Health: man has at least four more, and probably eight.

Senses No. 6 through No. 9 are found easily by breaking down the sense of touch into five separate senses: "crude" touch, pressure, heat, cold and pain. (Some authorities list four: "true" touch, temperature, superficial pain and deep pain.) Says Author David W. Foerster, a third-year medical student (University of Oklahoma) who has made a special study of the subject: "Ordinarily, when we feel an object, we bring into play three or four of these senses simultaneously . . . When we touch a hot stove, we experience heat, pain, crude touch and perhaps pressure."

The breakdown of touch is less a matter of semantics than of anatomy: each of these senses, says Foerster, "has its own receptor cells to receive impressions of the outside world, and its own nerve pathways."

Feel & Position. Nos. 10 and 11 are esoteric senses, little known but of great importance: vibratory and two-point discrimination sense. The vibratory sense is lodged in bone, which can feel the vibration of a tuning fork even when surrounding tissue cannot. Two-point discrimination (in itself a two-part sensory apparatus) can best be demonstrated with a schoolboy's compass whose steel and pencil points are an inch apart. Held against the back, this feels like a single object -the skin of the back has little two-point discrimination, and may need to have the compass spread three or four inches. But the hand can distinguish the two points when they are but a fraction of an inch apart--and there the senses of touch will also distinguish between the sharp steel and the duller pencil point.

Most complex of the additional senses, with more paraphernalia in the brain than even the sense of sight, is No. 12, proprioception or position sense. Test it thus: "Close your eyes and slowly lift your arm. Although you are able to feel no touch sensation, still you can sense your arm's changing position in relation to the rest of your body."

In the Canals. Easily identified and eminently useful is No. 13, the sense of equilibrium. Its most important receptors are three fluid-filled canals set in different dimensions in the labyrinth of the ear. This affords, says Foerster, "the ability to maintain balance even though our ears be plugged and our eyes closed . . . When the head or whole body is tilted, the fluid in the tubes is disturbed, setting up nerve impulses that let us know we are leaning to one side."

Aside from their everyday utility, man's additional senses are valuable in medicine, especially in diseases of the nervous system. Example: a lab assistant who took glassware out of a sterilizer developed blisters on his hands though he felt no heat on handling the bottles. Neurological examination showed no sense of heat or pain in his palms, but other senses were normal. Diagnosis: syringomyelia, a disease of the spinal cord. Its site was located because the neurologists knew that with only the hands affected, the trouble must be where sensory nerves from the palm reach the spinal cord.

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