Skin and touch
Aristotle of ancient greece listed the five main senses as sight,hearing,smell,taste,and touch.Unlike the other sense organs,the body part involved in touch is not concerned with sense alone.It has many other functions.Indeed it is the body's biggest organ-the skin. On an adult,this living,leathery overcoat weighs about 5 kg (11lb) and has an area of some 2 sq m (2.4 sq yd).Its tough surface layer,the epidermis,continually replaces itself in order to repair wear and tear,and keeps out water, dust,germs,and harmful rays like ultraviolet from the sun.Under this is a thicker layer,the dermis,packed with nerves,blood vessels,and stringy fibres of the body proteins,collagen and elastin.The dermis also assists in temperature regulation,by sweating (p. 39),and thrning pale or flushed.Skin was ignored by many great anatomists.They dismissed it as something to be removed in order to study the more interesting bits beneath.Like many other body parts,the invention of the microscope made the skin's fascinating details visible.