Our sense organs 45

glands, as well as blood capillaries and lymphatic
vessels. In contrast, the thickness of the outer
layer, the epidermis (Greek epi = upon, above;
derma = skin), is only between 0.07 and 0.12 mm.
Our skin separates our bodies from the outside
world. It encloses us, gives us our individual
shapes, protects us from intruders, cools or
warms us, and conserves our body liquids. Surprisingly,
it contributes about one sixth of our
body weight, although the epidermis itself
weighs only about 500 g. The total area of the
skin amounts to approximately 1.6 square
metres. It is watertight, washable, and elastic. The
skin is thickest on the palms of our hands and on
the soles of our feet, and thinnest in the armpits
and on the eyelids.
Our skin – by numbers: One square centimetre
of skin contains:
6,000,000 cells
100 sweat glands
15 sebaceous glands
5,000 sensory corpuscles
200 pain points (receptor areas)
25 pressure points
12 cold-sensitive points
2 heat-sensitive points
The most important property of the skin is that it
contains our sense of touch, which is located in
the dermal layer. The outer layer is insensitive,
rubs off easily, and causes the ring left in the
bath after bathing.
The sense of touch is difficult to investigate. All
the other senses have a definite key organ which
can be studied, but the skin is spread over the
entire body and cannot easily be delimited or
“switched off”. In the case of vision, scientists can
observe blind persons to learn more about seeing,
and they can study deaf people to learn
more about hearing. But this is impossible for the
sense of touch.
Touching is ten times as strong as verbal or emotional
contact. If touching were not pleasant,
living things would not procreate. If we did not
enjoy touching and caressing, there would be
no sex.
A foetus feels the moist warmth inside the womb;
it perceives the heartbeats and the internal
rhythms of its mother. The sense of touch is the
first sense to develop. It functions automatically,
before the newborn baby’s eyes even open to
observe the world.
It has been discovered that there are many more
kinds of receptors than the four basic ones
through which we experience warmth, coldness,
pain, and pressure. All the different tactile sensations
are more complex than these four, and they
cause us to respond variously.
Tactile experiences (Latin tactilis = touchable):
Mechanical stimuli cause several different sensations:
stroking, touching, vibration, pressure, and
tension. The fingertips and the tip of the tongue
are especially sensitive. The fingertips can feel a
sharp point if the impression is only 10 µm, and
in the case of a vibrating stimulus pressed into
the skin, can feel it even if this is less than 1 µm.
Other functions of the skin: In addition to its
important function as a tactile sense organ, there
are several others, of which only a few are mentioned
below:
1 The skin protects passively, as well as actively,
against injurious external influences. It can
destroy invading infective agents.
2 The skin plays an important role in controlling
the temperature of the body, which should not
deviate from 37° C because most organs function
optimally at this temperature. Heat loss can be
increased or reduced by increasing or reducing
the flow of blood through the skin’s network of
small blood vessels. About three quarters of the
heat loss is effected by radiation and conduction.
The other quarter is effected by the evaporation
of water, partly unnoticed through the skin and
the lungs, and partly by perspiration. The invisible
evaporation through the skin comprises one third
of the total dermal loss of water.
41