cr own readers

TOUCH. 225
feels warm and in th e other case cold, it is evident
that the skin is not a judge of th e act ual temperature
of things. It only informs us wh eth er heat
is coming to the skin, or wheth er heat is leaving
the skin. Thus lukewarm water gi\'es heat tal the
skin when the hand is cold, but it takes heat from
the hand which has previously been heated by hot
water.
6. A piece of iron and a piece of wood in the same
room app ear to the hand to have quite different temperatures.
The iron appears to be nuch the colder.
Th ey ar c really of exactly th e same temperature, as
a thermometer would show. The iron f eels colder
simply because it is a better carrier (or conductor) of
heat than t he wood, and 80 it draws the heat out more
quickly from the hand. In a very hot room, where
both the iron and the wood arc hotter than the hand ,
the iron f eels th e hotter of th e two, because it carries
more heat to the hand than the wood does.
7. The nerv es of heat and of cold do not pass to
all parts of th e skin. I Th ey ar e to be found only in
certain localiti es called th e " heat spots" and th e " cold
spots." The latter are most easy to find, and we can
map out th eir position in our own hands quite readily.
Take a pin, dip its head in water to cool it, and draw
th e head ' slowly along the back of th e hand. Su d­
denly here and there you will feel the cold of th e pin.
If you mar k one of th ese spots with ink, you will find
th at whenever th e pin is dra wn over it the same
feeling of cold is prod uced. You must not do it too
qu ickly, or too often, however, or th e pin will get
warm, and th e nerves of that spot will be exhausted
and become less f