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PROTECTING, SENSING, REPAIRING |
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Auguste Rodin's " la Cathdrale " Stone Sculpture Inventory
Scanning electron microscopy of fingerprint |
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READING AT YOUR FINGERTIPS
No animal has hands as well developed as those of man. The sculptor Auguste Rodin considered the hand to be the proof of the "divine creative force". He paid homage to this idea in his sculpture "The Cathedral", representing two hands facing each other, creating the shape of a vaulted arch. The hand is the organ devoted to prehension and touch. Touch can be sensed all over the body, but the real tact is concentrated in the hand and fingers, which move over an object to determine its volume, temperature, and nature. The fingers of man have epidermal and dermal folds which we call the fingerprint. These fingerprints are unique to each individual, and allow an increase in the surface area of the skin at the ends of the fingers greatly raising the number of sensory receptors present. The hand is also an organ which allows us to communicate. Deaf-mutes employ a sign language using their hands, the blind read Braille with their fingertips. Braille characters were invented by Louis Braille in 1829.
Braille consists of symbols in relief representing the alphabet, arithmetic symbols and musical notes. Each character is in the form of a matrix of 6 points (3 lines X 2 columns)
Braille. script Sample.
The visually impaired reader moves his fingers over the paper, detecting the points standing out in relief, and associates a combination of points with a letter then a word. The blind are capable of reading 150 words per minute (300 to 1,000 words per minute for sighted person).
The threshold of sensitivity of the skin corresponds exactly to the dimensions of a Braille character. The sensitivity of an organ is defined by the sensitivity threshold to a mechanical stimulation (entry of a point to a depth of 6 m) and the spatial discrimination threshold (separation measured with dividers). Lowest thresholds occur at the tip of the tongue and on the fingertips (1-3 mm). The fingers have a very high density of touch receptors, which has led to an over-representation of the fingers in the somato-sensory cortex. The threshold of sensitivity of the skin corresponds exactly to the dimensions of a Braille character. The detection of Braille characters depends entirely on Merkel cells and Meissner corpuscles. Merkel cells, which are stimulated by angles, points and curves, provide the spatial characteristics of the Braille symbols, while Meissner corpuscles supply the temporal information.
Because of the discrimination threshold, a Braille character is 4 mm x 6 mm, thus an A4 Braille page (21 X 29.7) only contains 27 lines of 30 Braille characters. A Braille book thus occupies 3 to 6 times more volume than the same document in normal script.
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