647. The nerves of the skin are the organs of the sense of touch and feeling. Through them we receive many impressions that enhance our pleasures, as the grateful sensations imparted by the cooling breeze in a warm day. In consequence of their sensitiveness, we are individually protected, by being admonished of the proximity of destructive agents.

In what season of the year is the coloring matter less in the white race? 645. To what is the color of the skin referable? 646. Why have the races of the torrid zone darker complexions than those of the temperate or frigid zones? What is this colored layer called by many physiologists? To what is the different hues in animals owing? 647. Of what use are the nerves of the skin?

_Ill.u.s.tration._ A man who had been afflicted some years with a severe disease of a portion of the brain and spinal cord, was deprived of feeling in the lower extremities. He was directed by his attending physician to use a warm footbath. Intending to follow the directions given him, he immersed his feet in boiling water, which he supposed of a proper temperature. While his feet were immersed in the water, he experienced no sensation of an unpleasant nature. On withdrawing them, he was astonished to find the cuticle separated from the other tissues, by the effusion of serum, and thus producing a blister over the whole surface.

648. Portions of the skin would suffer every day, were it not for the sentinel-like care exercised by the nerves, by which all impressions are transmitted to the brain. As the skin is continually exposed to the influence of destructive agents, it is important that the nerves, provided for its protection, should be kept in a healthy state.

649. A large proportion of the waste of the body pa.s.ses through the outlets of the skin; some portions in the form of oil, others in the form of water and carbonic acid.

650. The oil-glands secrete an oil, partly free and diffused, and partly mixed with alb.u.men. When the cells are fully formed, that is, fully distended, they yield their contents, and the fluid matter they contain is set free, and pa.s.ses along the tubes to the surface; this fluid matter const.i.tutes the oily element of the economy of the skin.

651. The uses of the unctuous product of the oil-glands are twofold: 1st. The protection; 2d. The removal of waste matter from the system.

In the exercise of these offices the oily substance is diffused over those parts of the skin which are naturally exposed to vicissitudes of temperature and moisture,--as the nose, face, and head;--to the injurious attrition of contiguous surfaces,--as the flexures of joints;--or the contact of acrid fluids,--as in the excoriations to which infants are liable.

Give the ill.u.s.tration. 648. Why is it necessary that the cutaneous nerves be kept in a healthy state? 649. Through what membrane does a large proportion of the waste material of the system pa.s.s? 650. What is the function of the oil-glands? 651. What are the uses of the oily product of these glands?

652. The oil of the unctuous substance is the princ.i.p.al agent in effecting these purposes: 1st. It prevents the evaporation or congelation of the water of the cuticle, which would cause it to become parched and peel off, thus leaving the sensitive skin exposed.

2d. It affords a soft medium to the contact of moving substances. 3d.

It repels moisture and fluids. 4th. The action of these glands removes the waste atoms and purifies the blood.

653. In considering the purpose of the oily matter of the skin, there are two situations in which it deserves especial remark. 1st. Along the edges of the eyelids, where it is poured out in considerable quant.i.ty. Here, it is the means of confining the tears and moisture of the eyes within the lids, defending the skin from the irritation of that fluid, and preventing the adhesion of the lids, which is liable to occur upon slight inflammation. 2d. In the ears, where the unctuous wax not only preserves the membrane of the drum and the pa.s.sage of the ear moist, but also, by its bitterness, prevents the intrusion of small insects.

654. The use of the perspiratory glands is to separate from the blood that portion of the waste matter which is carried off through the skin in the form of vapor. Sanctorius, a celebrated medical writer, daily, for thirty years, weighed himself, his food, and excretions. He estimated that _five_ of every _eight_ pounds of food and drink pa.s.sed from the system through the many outlets upon the skin. Many place the estimate much lower. All physiologists agree that from twenty to forty ounces of matter pa.s.s off from the skin of an adult every twenty-four hours.

652. What prevents the evaporation of the water of the cuticle? Give its 2d use. Its 3d. Its 4th. 653. What is said in reference to the distribution of the oily matter along the edges of the eyelids? In the ears? 654. Of what use are the perspiratory glands? How long did Sanctorius daily weigh his food, to ascertain the amount of secretion that pa.s.sed through the skin?

655. The average amount of perspiration is about thirty ounces; and it pa.s.ses off in such minute portions, and mixes so rapidly with the surrounding air, that it is not perceived. For this reason, it is called _insensible_ perspiration. When this excretion is increased, it forms into drops, and is called _sensible_ perspiration. The following experiments prove the existence of this excretion from the skin.

_Experiments._ 1st. Take a cold bell-gla.s.s, or any gla.s.s vessel large enough to admit the hand, and introduce it perfectly dry; at the same time close the mouth by winding a napkin about the wrist; in a short time, the insensible perspiration from the hand, will be seen deposited on the inside of the gla.s.s. At first, the deposit is in the form of mist; but, if the experiment be continued a sufficient time, it will collect in drops.

2d. Hold the apparently dry hand near a looking-gla.s.s, and the invisible vapor will soon be condensed, and cover the gla.s.s with a slight dew.

656. It is important that this excretion be maintained with steadiness and regularity. When the action of the perspiratory glands is suppressed, all the vessels of the different organs will suffer materially, and become diseased, by the redundant waste matter that should be carried from the system. If a person is vigorous, the action of the organs, whose functions are similar to those of the skin, as channels for the exit of waste matter, will be increased, and thus relieve the diseased state of the body. But the over-taxing of these organs, to relieve the system, often produces a diseased action in themselves.

What were his conclusions? 655. What is the average amount of perspiration every twenty-four hours? What is insensible perspiration?

What is sensible perspiration? How can the existence of the excretion of the skin be shown? Give the 2d experiment. 656. Why is it important that these excretions be maintained regularly?

[Ill.u.s.tration: Fig. 117. 1, 1, The lines, or ridges of the cuticle, cut perpendicularly. 2, 2, 2, 2, 2, The furrows, or wrinkles of the same. 3, The cuticle. 4, 4, 4, The colored layer of the cuticle. 5, 5, The cutis vera. 6, 6, 6, 6, 6, The papill. 7, 7, Small furrows between the papill. 8, 8, 8, 8, The deeper furrows between each couple of the papill. 9, 9, Cells filled with fat. 10, 10, 10, The adipose layer, with numerous fat vesicles. 11, 11, 11, Cellular fibres of the adipose tissue.

12, Two hairs. 13, A perspiratory gland, with its spiral duct. 14, Another perspiratory gland, with a duct less spiral. 15, 15, Oil-glands with ducts opening into the sheath of the hair, (12.)]

_Note._--Let the pupil review the anatomy and physiology of the skin from Fig. 117 or from anatomical outline plate No. 9.

CHAPTER x.x.xIII.

HYGIENE OF THE SKIN.

657. The sensibility of the skin, and the activity of the oil and perspiratory glands, are modified by the condition of the cuticle, the temperature of the skin and body, the purity and warmth of the air, and the character of the light to which the body is exposed. Thus, to maintain a healthy action of every part of this membrane, attention should be given to _Clothing_, _Bathing_, _Light_, and _Air_.

658. CLOTHING, in itself, does not bestow heat, but is chiefly useful in preventing the escape of heat from the body, and in defending it from the temperature of the atmosphere. In selecting and applying clothing to our persons, the following suggestions should be observed.

659. _The material for clothing should be a bad conductor of heat_; that is, it should have little tendency to conduct or remove heat from the body. This depends mainly on the property possessed by the material in retaining atmospheric air in its meshes.

660. _The material for clothing should not possess the property of absorbing and retaining moisture._ Dampness, or moisture, renders apparel a good conductor of heat; beside, if the perspired fluid, and the saline material it holds in solution, are readily absorbed by the clothing, they become sources of irritation to the skin with which the apparel comes in contact.

657-716. Give the hygiene of the skin. 657. What influences modify the action of the oil and perspiratory glands? To what must attention be given to maintain a healthy action of the skin? 658. What is said in regard to the clothing? 659. Mention a property that the material for clothing should possess. 660. What property in the selection of clothing should we avoid? Why?

661. _Furs_ contain a greater amount of air in their meshes, than any other article, and they absorb no moisture; consequently, as an article of dress, they are best adapted to those who are exposed to great vicissitudes of heat and cold.

662. _Woollen cloth_ retains more air in its meshes than any other article except furs and eider down, and it absorbs but very little moisture. These properties, together with its comparative cheapness, render it a good article of apparel for all cla.s.ses of persons. The only objection to its general use is, the disturbance of the electricity of the system, and the irritation to delicate skins from the roughness of its fibres.

_Observation._ Flannels are not only beneficial, during the cold season, in preventing colds and rheumatism, but they are of great utility in the warm season, in shielding the system from the chills at evening, that induce disease of the alimentary ca.n.a.l. Their general use among children and delicate females, would be a preventive of the "season complaints" prevalent in the months of August and September.

663. _Cotton_ contains less air in its meshes than woollen, but much more than linen. In texture, it is smoother than wool, and less liable to irritate the skin. This fabric absorbs moisture in a small degree.

In all respects, it is well adapted for garments worn next the skin.

When woollen flannels irritate the skin, they may be lined with cotton.

664. _Silk_ is not as good a conductor of heat as cotton, nor does it absorb moisture to any considerable degree; its texture is smooth, and does not irritate the skin; consequently, when the garment of this fabric has sufficient body or thickness, it is a good article for clothing. The greatest objection to its use is the disturbance of the electricity of the system, and its high price.

661. Give the properties of fur. As an article of dress, to whom are they best adapted? 662. Give the properties of woollen cloth. Is this a good article for clothing? What objection? What are the advantages of wearing flannels? 663. What are the qualities of cotton as an article of dress? 664. Of silk?

665. _Linen_ is not only a good conductor of heat, and consequently a poor article of apparel, but it likewise absorbs the fluids carried from the system by the agency of the oil and perspiratory glands. When garments are made of this material, the body is not surrounded by a layer of air, but by one of moisture. This still further increases its power to conduct heat from the system, rendering it a very objectionable article of apparel, even in warm weather and in hot climates, where the dress is usually thin.