the system, generally, which the safety valve has to the boiler of the steamboat, or railroad engine. As the steamboat boiler, under heavy pressure, would often burst, were it not for the safety valve, so will there be many explosions of the human body, if the skin ceases to perform its offices.

There is one qualifying remark necessary here. I do not mean to say that the boiler will burst under a momentary compression for the first time. I mean only, that, when the boiler has been strained repeatedly and long, the attraction of cohesion in its substance becomes so much reduced, that the pressure at length overcomes the resistance, and there is an outburst.

Hence it is, that, in order to perfect health, the skin must perform, unremittingly, its great work of depuration. To accomplish this, it must be plump, active, and energetic; and, with the aid of other organs, must keep up constantly, in the body, a strong centrifugal or outward tendency. This centrifugal tendency exists, moreover, in the greatest possible degree, when the skin best performs the work or offices assigned to it. It must absorb, secrete, excrete, and sympathize.

To understand well our subject, let us look briefly, in the first place, at the MECHANISM of the skin; then at its OFFICES; afterwards at its LAWS; and, lastly, at the penalties annexed to the violation of those laws; or, in other words, at its

DISEASES.

I. MECHANISM OF THE SKIN.

The skin is not a single layer, or membrane, but is made up of several. Different anatomists speak of a widely different number of these layers; but we usually say there are three; 1. The cuticle, or scarf skin; 2. The rete mucosum, or mucous layer; 3. The cutis vera, or true skin.

The cuticle is to the human body what the scarf covering of the shrub or tree is to the interior. It has no vessels or nerves of its own; and, consequently, has no life or feeling. It has only innumerable small openings. These openings, for want of a better name, are called pores. It is through them that the perspiratory fluid and the sebaceous matter (to be spoken of presently) find their way. They are hardly discernible by the naked eye.

The cuticle is said to be scaly in its structure. It is easily removed — almost without pain, and without shedding blood. Thus we sometimes graze our skin, and remove large portions of it in a moment. It is renewed very rapidly — almost as soon as it has been destroyed. It is also easily detached by a blister.

Immediately under the cuticle, or, as some say, forming a part of it, is a species of thin and delicate network, in which are numerous little cells, containing coloring matter. In the African it is black, in our own European race it is white, &c. This layer of the skin is called rete mucosum.

The cutis vera, or true skin,—that alone from which, by tanning, leather can be formed, is the third and most important of the several layers. It is principally by means of this and its machinery, that the skin performs its numerous and varied offices.

To give some faint idea of this layer or membrane, suppose only a square inch of it, while in healthful activity, could be brought to view through a microscope which magnifies three hundred thousand times, like Humboldt's, or many millions, like Lardner's. The vast amount of curious machinery would astonish, if not overwhelm, the mind. Why, the mechanism of a green leaf is astonishing; but that of the skin far more so.

Perhaps you have seen some huge factory,-say the gingham factory, at Clinton, Massachusetts, where, at one view, you can beholdabout an acre of spinning and weaving machinery, with the hundreds of operatives required to work it; or you may imagine yourself on the top of the famous Crystal Palace in New York, surveying the wonders collected there for public exhibition; or you may witness the dissection of a steam engine into its more than five thousand pieces; and yet, surprising and overwhelming as either view might be, what is it to the view alluded to through the micro

scope? What is it compared with the sight of hundreds of rivers of blood coursing their way, and that, too, side by side, in opposite directions, with hundreds of nerves, lymphatics, perspiratory vessels, sebaceous glands, &c.? Is it too much to say that in this little spot-this square inch of human skin there appears to be vastly more of living machinery than there is of dead machinery in a whole acre of spinning jennies and power looms? *

*Carpenter, in his Principles of Human Physiology, estimates the pores of the skin at seven millions, and "the length of the perspiratory

For here it is, as I just now observed, in the interior of this wonderful cutis vera, or true skin, that the various

offices of this part of the human mechanism are performed. From birth to death, moreover, -in sleeping and in waking,

- there is no suspension of the labor, unless in sickness or disease.

tubing" at one hundred and forty-five thousand eight hundred and eighty-three feet, or nearly twenty-eight miles. This, of itself, is something. It is seventy or eighty feet of tubing for a single square inch of skin.

The color and texture of this membrane, when the cuticle and mucous coat have been removed, are essentially the same. God has thus not only made of one blood all the nations of the earth, but, in strictness of physiological language, he has made them all of one skin.

The hairs do not originate in the skin, but merely pass through it. The nails are inserted into it, somewhat as the hand is inserted into a mitten or glove. The nail does not pass through it, like the hairs.

This whole triple membrane is connected loosely with the parts underneath it, by means of a cotton-looking substance, called, in the language of the books, cellular membrane. What appear like large veins in the skin, especially that of laborers, are usually found in this cellular membrane, underneath it.

Why the skin appears to be so much thicker on the back part of the body and limbs, and on the palms of the hands and soles of the feet, is chiefly because the cuticle, or scarf skin, is so much thicker there. On the feet of certain laborers who go barefooted, the skin seems almost like sole leather for thickness.

The surface of the human body, or, in other words, the extent of the skin, is generally spoken of, in books of anatomy and physiology, as being about fourteen or fifteen square feet, in an adult of ordinary size. Its thickness and consequent weight are very different, according to the difference of temperament, and various other circumstances.

II. OFFICES OF THE SKIN.

The first office or function of the skin which I shall mention is its power of absorption. It is able to absorb or imbibe