The application of cold or hot water to the skin, produces two
effects,--a primary and a secondary,--action and reaction.
If the water be _cold_, the _primary_ effect is to make the skin
cold. When the _secondary_ effect or reaction comes on, the skin
becomes _warm_. If _hot_ water be applied to the skin, the _primary_
effect is to make the skin hot; the _secondary_ effect, or
reaction, leaves it cold.
The first effect is a momentary one; the second effect, or reaction,
continues a long time.