This, however, is injurious to the lungs, for it allows the blood to stagnate in them.

Exercise is Nature's method of compelling ventilation in the lung area.

Deep breathing may be used as a substitute, but the other beneficial effects of exercise are lost.
The skin and the various glands connected with it form a complex organism, the functions of which play a very important part in the work which the body has to do.

The skin aids the lungs in their work of respiration; and, like the lungs, it throws off water and carbon dioxide and absorbs oxygen.

The respiratory work of the skin, however, is only a minute fraction of that which the lungs do.
The skin is a heat regulator, and in this, its most important work, it is aided by the two million or more sweat-glands which are distributed over almost the entire surface of the body.