페이지 이미지
PDF
ePub

furnished by a minute capillary network of blood vessels arising from arterial trunks, which bring the blood to the gland to be purified, and terminating in venous trunks, which carry off the blood when that process has been performed.

These glands are consequently to be regarded as true excretory organs, removing from the blood materials that are no longer wanted, and which, if retained, would be injurious. Their size varies in different situations, being in the palm of the hand from 1-100th to 1-200th of an inch in diameter, but in the armpits, where they are largest, and form a very thick layer, they reach the size of 1-60th of an inch. Their ducts are composed of basement membrane and epithelium only; the latter being an inflection from the scarf skin which runs down the wall of the duct. The length of the tube which constitutes both gland and duct is about a quarter of an inch. It is straight while passing through the true skin; but becomes strongly spiral while traversing the scarf-skin, the turns being as close and regular as those of a screw. The diameter of this tube is about 1-1700th of an inch. We can have little idea of the importance of these little ducts to the system from considering any single one of them ; but when we come to consider them collectively, we may in some degree estimate their value, and the necessity of maintaining their functions in healthy action. Over 3,500 of these little ducts have been found to exist in a single square inch of the skin of the palm ; and accordingly, taking the length of each at a quarter of an inch, as we mentioned above, we find that their aggregate length amounts to 73 feet. On a square inch of the heel the length would be about 47 feet. About 60 feet would represent the average length of these ducts for a single square inch of skin for the whole body; and as the number of square inches in a person of ordinary size is about 2,500, we arrive by computation at the startling result, that the aggregate length of the sudoriferous ducts of the body is about 28 miles.

It was to this glandular system we referred, when we said there was a beautiful contrivance for regulating the internal temperature of the body; for the perspiration so poured out is vaporised principally by the heat of the body ; and in thus turning into vapour it renders latent, as all liquids do in undergoing that change, an enormous amount of heat, which is thus being constantly carried away from the body as fast as it is generated by the chemical processes constantly going on within the system. Hence we see the cause of that burning heat of skin which is so marked a symptom of some diseases when the perspiration is completely arrested, causing that peculiar harsh, dry skin, which is so well known to the physician as the concomitant of this burning heat.

It is due to the same cause that the blood never exceeds about 989 Fahr. in temperature, even under violent exercise ; for a copious flow of perspiration carries off the heat so generated. And for the same reason it is possible in dry air to bear with impunity a degree of heat much beyond what could be borne in moist air, where the perspiration would not be vaporised as fast as excreted. Water, at the temperature of 120° is almost unbearable. A vapour bath at the same temperature might be endured for a few minutes; but the distress arising from the suppressed perspiration would soon render it intolerable. But in dry air a heat can be borne with impunity, and almost without discomfort, which will roast eggs and dress beafsteaks. In some experiments performed by Drs. Watson and Carpenter, it became desirable to ascertain the height at which a thermometer stood in an oven, without subjecting it to the cooling consequent on withdrawing it. A girl volunteered to go into the oven and mark the height of the mercury. The gentlemen hesitated at her proposal; but she assured them she was not in the least afraid of so doing; and she actually went in, and remained there for ten minutes, while the thermometer stood at 280°; and another girl remained for five minutes in the oven with the thermometer at 325°, or 113° above the point of boiling water. Beefsteaks were cooked in this oven, merely by the temperature of the air, in thirty-three minutes; and when the air was blown on them by a pair of bellows, they were cooked in thirteen minutes. And yet in these experiments the young women suffered scarcely any inconvenience; and the heat of the body, as tried by a thermometer placed under the tongue, was scarcely at all increased. Sir Charles Blagden remained for some minutes in air of about the same temperature, and also Dr. Lankester; and Chabert, the French showman, called the Fire King, was in the habit of entering an oven

of molten lead. Animals covered with hair or feathers, however, die very soon in temperatures much below these; apparently because the hair or feathers interfere with the free escape of moisture from the skin, which is necessary to keep the blood cool, and prevent injurious consequences. Hence, also, persons who are in the habit of taking Turkish baths, which are, in fact, hot-air baths, experience no inconvenience from the high temperature as soon as the perspiration begins to flow, which, in a practised bather, it does immediately.

the pores during the twenty-four hours is not less than an imperial pint, containing about an ounce of solid matter in solution, and besides a large amount of carbonic acid gas: hence we can estimate the importance of keeping these ducts in perfect order by means of frequent bathing.

Another kind of gland is also found in the skin in connection with the hairs, and engaged in their nutrition. These glands are called the sebaceous glands, inasmuch as they furnish an oily or waxy substance to nourish the hairs; this substance is developed in largest quantity inside the ear, where it serves to prevent access of dust, insects, &c., to that delicate organ. The ducts of these glands are not spiral, and they open generally into the hair follicles, or pits which the hair grows out of, situated in the subcutaneous areolar tissue.

There are generally several glands connected with each hair; their ducts are frequently inhabited by a very peculiar little parasite, by no means a beautiful object when viewed under the microscope, but found even in the cleanest and healthiest persons, sometimes three or four being in each follicle ; yet they are specially found in persons whose skin is torpid in its action, and they multiply in sickness. These glands lubricate the skin, and so maintain its elasticity, and they also serve to eliminate hydrocarbons from the system ; they are extremely numerous, as may be inferred from their connection with the hairs.

We may here mention briefly the structure of hair, as being connected with these follicles. Hair may be regarded as a kind of modified cuticle, though it takes its origin much deeper than the cuticle, and even deeper than the true skin. The scales of the epidermis descend into the hair follicle, forming its lining, and then, at the bottom of the follicle, the cells which on the surface would become cuticular scales are changed into a layer of imbricated or overlapping scales, which form the cortex or bark of the hair; while the cells which grow from the very bottom of the follicle are modified into elongated fibres, and so form the inner substance of the hair.

A very curious and beautiful structure is especially developed around the hair follicles and sebiparous glands, consisting of minute, quite microscopical muscular fibres, not capable of being acted on by the will, but acting involuntarily on the application of certain stimulants, external or mental; cold, fear, anger, &c., will stimulate these fibres to contraction, and hence, owing to their peculiar interlacing around the hair follicles, arises the peculiar bristling so well seen in some animals, particularly the lion and others of the cat tribe, under the influence of these emotions. To this cause also is due what is known as the hair standing on end, the first notice of which we have in the Book of Job-" Then a spirit passed before my face; the hair of my flesh stood up.” The creeping of the flesh under the same emotions is due to the same cause ; for, although particularly well developed around the hair follicles, these muscular fibres are not confined to them, but extend everywhere through the skin, and the appearance assumed by the skin under the influence of cold, and known as the “goose-skin,” is due also to their contraction.

Hair is almost universally the covering of the skin in the class of Mammalia, and is found even in the whale, but only in the shape of a few scattered hairs here and there over the body, so that it can be of no use except to carry out the type of the organisation of the class. In certain parts of the bodies of some animals hairs sometimes become remarkably developed and strangely modified, as is the case in the hedgehog and porcupine, where they assume over the greater part, but not the whole of the body, the form of spines and quills.

In the class of birds hair is not found, being replaced by feathers, and the apparent hairs on animals of this class, on being examined with a microscope, present the characters of feathers, and not those of hair.

We have thus sketched the principal characters of that beautiful organ, the Skin, which, it is hardly necessary to observe, is as completely illustrative of the Creator's skill and wisdom as is every other portion of the animal frame.

feathere have the skilustra

EXPLANATION OF PLATE XVI. Fig. 1. Vertical section through skin of thumb. a. Horny layer of epidermis ; b, its mucous layer ; c, the corium ; d,

fat globules ; e, sudoriparous glands; f, their canals ; i, sweat

pores. Fig. 2. Compound papilla, from the hand. Fig. 3. Section through the skin, from the leg of a negro; a, horny layer of

epidermis; b, mucous layer ; C, coloured cells of the mucous layer ;

d, papillæ. Fig. 4. Termination of a nerve in a Pacinian corpuscle, from the hand; A,

nerve; B, envelope. Fig. 5. Perpendicular section through the scalp, with two hair-sacs ; ly

epidermis ; b, muscle of the hair-follicle; c, cutis. Fig. 6. Under-surface of the epidermis, from the palm, showing the depres

sions in which the papillæ were lodged, and the sudoriparous ducts

attached. Fig. 7. Section through the skin, near the ear. a, horny layer of epidermis;

b, sebaceous glands ; c, canal of; f, ceruminous glands ; d, hair

follicle ; 9, fat globules. Fig. 8. Hair-sac, from the face, with several specimens of Demodex follici

lorum attached Figs. 9, 10. Demodex folliculorum.

Figs. 1–7 are after Kolliker (Hum. Hist.)
Figs. 8--10. E. Wilson, in Proceedings of Royal Society,

THE FURNITURE WOODS OF COMMERCE.

BY P. L. SIMMONDS.

THE commerce in Foreign Woods carried on by this country

1 is much larger than would be supposed by those who had not looked into the figures; and the vast quantities of timber, useful and ornamental, received, form a very interesting subject of inquiry. The timber of many countries is a most important item in its annual income, especially in Russia, Austria, Norway, Switzerland, Brazil, and also in British North America, India, Guiana, and some other of our possessions. The value of the woods of all kinds that we import is not less than twelve millions sterling, whilst about four millions more may be set down as the value of the home produce. These woods, as far as their economic uses are concerned, are divided into three classes :1st.-Woods of construction, useful for ship and house build

ing and other rough work. 2ndly.-Those suitable for cabinet and ornamental work, as

tables and other articles of furniture, pianofortes, &c. 3rdly.—Dye-woods, and many hard woods, used chiefly by

the turner, carver, engraver, &c. To the first class belong such woods as the fir, and indeed all the Coniferæ, if we except the evergreen cypress, whose beautiful colour and pleasing odour fit it in an especial manner to rank among the higher class of cabinet woods. To this division belong also the beech, ash, chestnut, poplar, and willow ; while teak, oak, and plane-tree would seem to occupy a middle class, connecting this with the second, or more ornamental woods, among which are ranked mahogany, rosewood, walnut, maple, laburnum, mountain ash, box, &c.

It is to the Furniture Woods that we purpose confining our present observations, and chiefly to those received from foreign countries.

The importance of this survey will be better appreciated when it is stated that the annual value of the household furniture made in this country alone was, more than ten years ago, estimated at fifteen millions, and has certainly largely increased since then, keeping pace with the wealth and numerous wants of the nation, and progress of commerce. The computed value of the rough fancy hard woods imported in 1861 was £804,426,

« 이전계속 »