It has been shown that the perspiration-tubes are coiled up into a
ball at their base. The number and extent of these tubes are
astonishing. In a square inch on the palm of the hand have been counted,
through a microscope, thirty-five hundred of these tubes. Each one of
them is about a quarter of an inch in length, including its coils.
This makes the united lengths of these little tubes to be seventy-three
feet to a square inch. Their united length, over the whole body is
thus calculated to be equal to _twenty-eight miles_. What a wonderful
apparatus this! And what mischiefs must ensue when the drainage from the
body of such an extent as this becomes obstructed!
But the inside of the body also has a skin, as have all its organs.
The interior of the head, the throat, the gullet, the lungs, the
stomach, and all the intestines, are lined with a skin. This is called
the _mucous membrane_, because it is constantly secreting from the blood
a slimy substance called _mucus_. When it accumulates in the lungs, it
is called _phlegm_. This inner skin also has nerves, blood-vessels, and
lymphatics. The outer skin joins to the inner at the month, the nose,
and other openings of the body, and there is a constant sympathy between
the two skins, and thus between the inner organs and the surface of the
body.
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