sink into the fabric, nor so clinging as to resist easy removal by the broom.
It is manifest, however, that the mechanically held dirt which we have been considering differs very considerably from the dirt on our skins, and on linen in contact with our bodies, which, although derived from the same sources as the dust on the furniture, resists any ordinary mechanical process for its removal, and rinsing dirty hands or linen in cold water has but little cleaning effect, while if the hands are afterward dried in the usual way a transfer of a portion of dirt to the towel takes place. If we carefully notice the portions of our skin and shirt which become most soiled, we at once observe that it is where the skin is exposed to air, while the linen, which is in contact with both air and skin, becomes dirty more quickly than when exposed to either alone.
The part played by the atmosphere is made clear by the facts which we have already been considering, but the action of the skin introduces a new and most important factor. For the healthy carrying on of the functions of life, nothing exceeds in importance the skin with which our body is covered. We may live for days without giving our stomach any work to do, the liver may cease action for several days before death ensues, but it is impossible to survive for the same length of time if the functions of the skin are entirely stopped. The skin not only plays an important part in throwing off and getting rid of waste matter from the system, but it is also credited with being an important auxiliary to our lungs; and experiments have clearly shown that if the skin of animals be coated in such a way as to completely stop its action, a very few hours will bring about death.
If we examine the structure of the skin, we find that it is built up of two distinct layers, an outer skin called the cuticle or epidermis, and an inner termed the cutis or dermis. A third layer intermediate between these two used to be looked upon as a third skin, but more recently has been recognized as being only a transition form-of the outer skin. The cuticle or outer skin consists of several fine layers of scales which gradually assume a more rounded and granular form the deeper one gets into the cuticle. These rounded granules form the middle skin of the old observers, and as the outer portion of the cuticle roughens and scales off as scurf, these granules gradually flatten and form the new surface to the outer skin; and we differ therefore from other scaly reptiles by being continually in a condition of renewing our skin, while most reptiles and fish cast their scaly covering in one operation.
No nerves or blood-vessels find their way into this outer skin, as may be seen when it becomes detached from the inner skin in the formation of a blister, the outer portion of which is devoid of sensation. The lower or true skin varies in thickness, being
