THE

PHRENOLOGICAL JOURNAL.

No. XXXIV.

ARTICLE I.

NATURE AND USES OF THE SKIN, AS CONNECTED WITH THE PRESERVATION OF HEALTH.

In the thirst for knowledge which characterizes the present generation, the structure and functions of the human body have been as much overlooked by the general reader, as if the subject were destitute of interest in itself, and of no utility when known and hence we have the singular anomaly before us of highly educated men-men who are conversant with the natural history of the mineral and vegetable kingdoms, and with the structure and habits of the lower animals-displaying a degree of practical ignorance in regard to their own bodily and mental constitutions, which would excite astonishment were it not so common. The evils attending this state of things are incalculably great, not only as involving the security of health and the happiness of families, and perpetuating the destructive reign of the quack; but as retarding the progress of the race in the improvement of their physical, moral, and intellectual conditions. Public attention is, however, awakening to the necessity of knowing something of ourselves; and a multitude of remarks soliciting information on the subject are now to be met with in many of the journals and cheap publications of the day. We propose to contribute our mite to the common stock, and shall begin with offering a few observations on the functions of the skin; carefully avoiding what is either too technical or too abstract for general comprehension.

VOL. VIII.-NO. XXXIV.

A

Structure of the Skin.-The skin is that covering which in man and animals protects the whole surface of the body, and preserves it from the too rude contact of external objects. Like every other part of the animal frame, its structure displays the most striking proofs of the transcendant wisdom and beneficence of its great Creator. Simple in appearance and in design, it is, in fact, a compound of many elements, and the seat of as great a variety of functions. It is composed of three layers of membrane: the outermost is the thin scarf-skin, epidermis, or cuticle, which rises in blisters, and is so easily abraded by violence; the next is the soft mucous layer or coat, which is the seat of colour, and which in the Negro is of a dark colour; and the inner is the thick true skin, as it is called, which immediately encompasses the body, binding every part in its place. These distinctions should be kept in view, for, as it is a general law, amply illustrated by Phrenology, that every part has a use or function peculiar to itself, the combined uses of the compound can be understood only by attending to those of the simple elements.

Cuticle or Scarf-Skin.-The scarf-skin forms the outermost layer. It has no perceptible nerves or blood vessels, and consequently it neither bleeds nor feels pain when cut or abraded. Such being its constitution, it is appropriately placed on the outer surface, because it may come into contact with rough bodies without injury; while its intermedium serves to soften the impression made on the more sensitive parts beneath, and it is sufficiently thin to allow every inequality to be felt distinctly by the nerves of the true skin, and the requisite information to be conveyed to the mind. From its quality of becoming thicker when much brought into use, it forms an admirable protection to the skin beneath. Were this not so, it would be impossible for us to walk on our feet, or to work with our hands, without pain. In infancy, the cuticle on the soles of the feet is nearly as thin, and the surface consequently as sensitive, as on any part of the body; and in proportion as the strength increases, and the child begins to walk, the cuticle begins to thicken and harden, so as to protect the feet from being hurt by the inequalities of the soil or the pressure of the shoes. It may be remarked, that the cuticle covering the arch of the foot remains thinner than the rest, because there external pressure operates least; and that it becomes very thick on the heel, particularly in those who walk much, because the heel forms the principal support of the body, and is most in contact with the ground. In like manner the sensitive skin of the hand is defended by a cuticle, thick in proportion to its wants. In the delicate lady, who wields no implement heavier than her needle, it is thin and pliant; while in the blacksmith and labourer, whose occupations

would tear in pieces the thin cuticle of the lady, it is thick and hard, forming as it were a protective cushion for the true skin below. Being destitute of blood vessels and of nerves, and apparently also of life, it may be cut or torn without pain; and when removed by vesication or by burns it is speedily renewed. For the same reason it resists putrefaction for a long time, and is found unchanged in bodies which have undergone extensive decay. Homogeneous in structure, it is supposed to be perforated by numerous holes, to allow the hairs and perspiration to pass through, although these are so small as not yet to have been demonstrated. By preventing the perspiration from passing off too rapidly by simple evaporation, the cuticle subserves the purpose of preserving the true skin in that moist and pliant state which is essential to the due exercise of touch and sensation. Its uses, therefore, are twofold,-1st, The protection of the skin from the rude contact of external bodies; and, 2d, The preservation of its requisite degree of moisture and softness. The nails belong to the cuticle, and like it are insensible to pain, and regenerate on being destroyed.

Mucous Coat.-The middle or mucous coat of the skin need not occupy much attention, for it is still in dispute whether it be really a membranous expansion or merely a mucous secretion. Some anatomists have considered it to be composed of several distinct layers; while others think it a mere secretion, and destitute of organization. Being the seat of colour, it is thickest in Negroes and the coloured races of man, and is not perceptible in the Albinos. From all that is known regarding it, it may be viewed generally as merely a thin soft covering placed between the outer and the inner skin, to protect the nerves and vessels of the latter, and give them their requisite softness and pliancy.

True Skin. The third or inmost layer, called the true skin, dermis, or corion, constitutes the chief thickness of the skin, and is by far the most important of the three both in its structure and functions. Unlike the scarf-skin and mucous coat, which are homogeneous in their whole extent, and apparently without organization, the true skin, or simply, as we shall call it for brevity's sake, the skin, is very delicately organized, and endowed with the principle of life in a very high degree. Not only is it the beautiful and efficacious protector of the subjacent structures, but it is the seat of sensation and of touch, and the instrument of a very important exhalation, viz. perspiration, the right condition or disturbance of which is so powerful an agent in the preservation or subversion of the general health. It is of a fibrous cellular texture, and its looser internal surface, which is closely united to the cellular membrane in which the fat is deposited, presents a great number of cells or cavities, which

penetrate obliquely into the substance and towards the external surface of the skin, and also contain fatty matter. These cells are larger on some parts of the body than on others, and are very small on the back of the hand and foot, the forehead, &c., where fat is never deposited, and the skin is consequently very thin; while they are large in the palm of the hand and sole of the foot, where the skin is consequently thicker and fat abounds. These cells or cavities are traversed by innumerable blood vessels and filaments of nerves, which pass through to be ramified on the outer surface of the skin, where they shew themselves in the form of numerous small papillæ or points, which are very visible on the surface of the tongue, and on the fingers and palm of the hand. These papillæ constitute the true organs of touch and sensation, and are therefore most thickly planted where these

senses are most acute.

The true skin is so abundantly supplied with blood and nervous power, that, for practical purposes, it may almost be regarded as composed of vessels and nerves alone; and it is important to notice this fact. The universal and equal redness of the skin in blushing is itself a proof of great vascularity; but a still stronger consists in our being unable to direct the point of the finest needle into any spot without puncturing a vessel and drawing blood. The same test proves the equal abundance of nervous filaments in the skin, for not a point can be punctured without transfixing a nerve and causing pain; and it is well known that, in surgical operations and accidental wounds, the chief pain is always in the skin, because it is profusely supplied with nerves on purpose to serve as the instrument of feeling. From these examples, the skin may be truly considered as a network of blood vessels and nerves of the finest conceivable texture; and taking the vast extent of its whole surface into account, we can easily understand how these minute ramifications may really constitute a larger mass of nervous matter than is contained in the original trunks of the nerves from which they are incorrectly said to arise, and also how so large a proportion of the whole blood may be circulating through the skin at one time.

Uses of the Cuticle.-We must next study the uses to which these structures are subservient in the animal economy; and to understand them thoroughly, let us recall to mind the principle already mentioned, that every part has a function appropriated to itself, and that consequently, where more than one function appears, there must be complexity of structure. apply this principle to our present subject, we have first the cuticle or scarf-skin serving physically as a defence against external friction and injury to the softer parts beneath, and becoming thicker wherever the friction is increased so gradually as to ad

To

mit of its formation. But, if too great friction be applied suddenly to parts unused to it, and time be thus not given to the cuticle over them to become thicker, the tender parts being inadequately protected, become irritated and inflamed, and throw out a quantity of watery fluid or serum on their surface, which raises up the cuticle in blisters, and, by making it painful to continue the pressure, obliges the person to desist from an exercise which, if continued, would evidently soon alter the structure of the sentient nervous filaments, and unfit them for their proper uses. In like manner the cuticle, by impeding undue evaporation from the surface of the true skin, preserves its softness and pliability; whereas, were the cuticle wanting, the skin below would become dry and hard by exposure to the air, and altogether unfit for its purposes.

Uses of the Mucous Coat.-The chief use of the mucous coat also seems to be the protection of the delicate structure beneath it. Being of a dark colour in the Negro, it is believed to diminish the influence of the sun's rays in tropical climates by the higher radiating power which is possessed by a black than by a light surface. It is the mucous coat which is the seat of the variegated colouring observable in the skins of many of the lower animals.

Uses of the true Skin.-To understand the important purposes of the true skin, we must distinguish between its constituent parts, and consider it in virtue of each of them,-1st, As an exhalant of waste matter from the system; 2dly, As a joint regulator of the heat of the body; 3dly, As an agent of absorption; and, 4thly, As the seat of touch and sensation.

The Skin considered as an Exhalant.-Every body knows that the skin perspires, and that checked perspiration is a powerful cause of disease and of death; but few have any just notion of the real extent and influence of this exhalation, such as we shall attempt to exhibit it. When the body is overheated by exercise in warm weather, a copious sweat soon breaks out, and, by carrying off the superfluous heat, produces an agreeable feeling of coolness and refreshment. This is the higher and more obvious degree of the function of exhalation; but, in the ordinary state, the skin is constantly giving out a large quantity of waste materials by what is called insensible perspiration, a process which is of great importance to the preservation of health, and which is called insensible, because the exhalation being in the form of vapour, and carried off by the surrounding air, is invisible to the eye; but its presence may often be made manifest even to sight by the near approach of a dry cool mirror, on the surface of which it will soon be condensed so as to become visible. The average amount of the insensible perspiration in twenty-four hours has been variously estimated; but so many