The performance of our sensory devices:
- Human eye: can theoretically see a lighted candle in perfect darkness at 30 km!
- The human ear: on average can record sounds with a height of 20 to 20,000 hertz, equivalent to about 10 octaves; an exercised ear can distinguish a murmur at 100 m and distinguish several thousand different sounds, and two different sounds of 1/300 octave!
*Our tongue: can detect a solution of HCl diluted to 0.0001 mol / liter, a saline solution of 0.002 mol / liter NaCl, a sucrose solution of 0.0125 mol / liter, the bitterness of quinine at 0, 0000015mole / liter. It is between 20 ° C and 35 ° C that our food has the most flavor, from where the ability to eat hot and to order some Wines.
- Nasal mucosa: is noticeably sensitive: 6 mg of ether in one liter of air, we can distinguish between 2000 to 4000 different odors, but many animals have a much more developed sense of smell.
- The skin: is sensitive to temperature variations of 1/10 degree C, but this sensitivity is unequally distributed; The tip of the fingers is more sensitive to the touch than the base of the fingers or the palm of the hand; The back of the hand is more sensitive to the warmth than the palm of the hand. The tactile acuity of the blind is remarkable, they can read with the fingers of the characters in relief (Braille characters).