Evaporation and perspiration are practically one and
the same thing. , Hence, we see that by this insensible
perspiration the heat of the body is dissipated. When
we undergo violent exercise we generate heat rapidly
in the, body. This must make its escape rapidly. In
this case the perspiration or evaporation of water from
the surface of the body becomes excessive, showing
itself in the profuse perspiration \7hich occurs during
vigorous exercise. It is the insensible perspiration
which is of importance to us. The texture of the
garment worn next to the skin should be such as will
in the least degree interfere with this physiological
process. If we examine the fibre of the different fa-
brics which are worn, viz. : cotton, silk, linen and wool,
we will find a very notable and striking difference be-
tween the first three of these and the last. The fibre
of cotton, silk and linen is an absolutely straight, in-
elastic fibre. When woven into a textile fabric the
result is a somewhat dense, felt-like, impermeable
cloth. As the result of this impermeability, when
worn next to the skin, it has a tendency to hamper
and interfere with this process of insensible perspira-
tion or heat-radiation. If, on the other hand, we ex-
amine the wool fibre, we shall find a highly elastic,
curling fibre, being absolutely unique and differing
■from all other fibres in this respect. When woven



into a textile fabric, wool makes a highly elastic and
exceedingly porous cloth, which, when worn next to
the skin, interferes with this process of insensible per-
spiration or heat-radiation less than any other known,
textile fabric. Hence, the underwear should be
made of pure wool, as affording a fabric incompara-
bly superior to all others.
