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another set of tubes called veins, and by them brought back again to the heart.

467. Thus, there is a constant circulation, outward and inward, of this same blood, at the rate of an ounce to each contraction, from the heart through the arteries and back to the heart by the veins. To warm, revive, nourish it, and keep up its quantity, there are various other wonderful, but very simple contrivances.

Were once the energy of air deni'd,

The heart would cease to pour its purple tide;
The purple tide forget its wonted play,

Nor back again pursue its curious way.

468. The heart consists of four cavities, from one of which called the left ventricle, the blood is driven into the arteries through the body; by another, called the right auricle, it is received back again by the veins: it then passes into the right ventricle, whence it is forced into the lungs.

Having there been revivified by coming into contact with the air, it is carried back by a set of veins into the left auricle, and, from thence into the left ventricle, where it began its course: it is then again forced into the arteries, brought back by the veins, &c. till the end of life.

469. The lungs are large and spongy substance filling nearly the whole cavity of the chest, which rises as they fill and falls as they empty, in respiring air through the mouth or nostrils.

The act of respiration is performed about 20 times in a minute; and about 40 cubic inches of air are respired every time; of which 2 inches of oxygen are absorbed by the blood on the lungs, producing at the same instant, 98 degrees of vital heat, and restoring the veinous blood to its bright red colour.

Obs. The lights used in families to feed cats, are the lungs of sheep or oxen, and are exactly similar to the lungs of man. On inspection, they will be found to be wonderfully adapted to their design of bringing the air in contact with the blood.

Any rupture in this tender fabric, or defect in their action, leads to that fatal class of diseases, called Consumption.

470. Four thousand times in every hour, each caviity of the heart is called into action: and all the blood in the body passes through the heart 14 times in every hour.

The arteries, into which it is forced, branch in every direction through the body, like the roots, banches, and leaves of a tree, running through the substance of the bones, and every part of the animal substance, till they are lost in such fine tubes as to be wholly invisible.

471. In this manner, they distribute nourishment; supply perspiration; and renew all the waste of the skin; and, by passing through glands in every part of the body, all the various animal secretions are elaborated.

In the parts where the arteries are lost to the sight, the veins take their rise, and in their commencement are also imperceptible. The blood is then of a dark colour; and, as it returns to the heart with a less impetus, there is always twice as much blood in the veins as in the arteries.

472. As the blood, in this discoloured state, has lost some of its vital power, it is driven through the lungs, and its colour is restored, but on its passage back to the heart, it also receives a supply of a new fluid extracted from the food of the animal in the stomach and intestines.

The loss of weight in a human body by perspiration in 24 hours is about four pounds; and what is gained by the inspiration of air into the lungs, is lost by the expulsion of moisture, and of gas generated in the lungs.

473. The motion of the lungs is preserved by that of the chest containing them; that of the heart, may be felt on the left breast; and the circulation of the blood, by the action of the pulse in various parts of the body, and particularly at the wrist,

In children, the pulse gives 120 strokes in a minute; at 20 years, about 75; at 30, about 70; and in old age, 60 or 50.

474. For the purpose of renewing and nourishing the blood, food is taken in at the mouth, macerated by the teeth, and mixed with the saliva; it is then carried into the stomach, (a bag like a highland bagpipe,) where it is dissolved into a soft pap by a powerful liquid called the gastric juice.

475. This pap is then drawn from the stomach into the intestines; where, by means of a liquid called bile, it is separated into a white milky liquid called chyle, and into the excrement.

The chyle is taken up, or absorbed, by myriads o fine tubes called the lacteals, which carry it to a main pipe called the thoracic duct. This pipe ascends to the throat, where it empties the chyle into a large vein, and being mixed with the blood, is conveyed to the heart.

476. Of such subtle and wonderful contrivance is the organization of man! Similar, also, is the construction of the whole of animated nature, from the greatest to the smallest.

Within the package of the skin, and essential to life and comfort, are numerous bones for strength; hundreds of muscles and tendons for action; nerves spread every where for sensation; hundreds of arteries, to carry out the blood; hundreds of veins to bring it back again; and hundreds of glands performing all kinds of secretions; besides an infinite number of tubes called lacteals and lymphatics, to absorb and convey nutriment to the blood.

477. Such being the complex construction of animal bodies, is it not rather wonderful that we last 70 or 80 years, than that we endure no longer! When it is considered also, that a muscle or a bone out of place, a vein or artery stopt in its circulation, or a nerve unduly acted upon, creates disease, pain, and misery; is

it not wonderful, that we enjoy so large a portion of health and pleasure?

Should not such considerations teach us the value of prudence and temperance?

Thick, in yon stream of light, a thousand ways,
Upward, and downward, thwarting and convolv'd,
The quivering nations sport; till, tempest-wing'd,
Fierce Winter sweeps them from the face of day;
E'en so, luxurious men, unheeding pass
An idle summer-life in fortune's shine!
A season's glitter! Thus they flutter on
From toy to toy, from vanity to vice ;-
Till, blown away by death, oblivion comes
Behind, and strikes them from the Book of Life.

THOMSON.

478. The nerves are soft white chords which arise from the brain, the focus of sensation, and disperse themselves in branches through all parts of the body. Impressions are recieved by the brain from the adjacent organs of sense; and the brain exercises its commands over the muscles and limbs by means of the

nerves.

Thus, the body is enabled to avoid what is hurtful, to flee from danger, and to pursue every thing useful and agreeable.

Obs. Trees and vegetables have no nerves or sensorium; because, as they are unable to move and avoid danger, they could be of no use to them. The proper object of vegetable organization, appears to be to supply food to animated nature; and the wisdom of Providence is in nothing more evident than in the variety, wholesomeness, and abundance of vegetable provisions.

479. The ear is placed in the most convenient part of the body near the brain, the common seat of all the senses, to give more speedy information.

In man it is of a form proper for the erect posture of his body; in birds, of a form proper for flight, and not protuberant; in quadrupeds, its form is, in some, large, erect, and open; in others, covered; in subter

raneous quadrupeds, the ears are short and lodged deep.

480. The structure of the ear is admirably contrived to collect the undulations of sound, and to convey them to the sensory in the brain. The first part is the auricle, or external ear, formed to stop and collect the sonorous undulations, and convey them to the concha, or large capacious round cell, at the entrance of the ear. Persons, whose ears are cut off, have a confused hearing, and are obliged to form a cavity round the ear with their hand.

In the interior is the auditory passage, curiously tunnelled and turned, to give sounds an easy passage, and prevent their too furiously assaulting the more tender internal parts.

481. To prevent the entrance of noxious insects, this passage is secured with a bitter nauseous substance, called ear-wax. The next principal part is the membranum tympani, or drum of the ear, with its inner membrane, the four little appendant bones and the three inner muscles to move them, and adjust the whole system to hear loud or soft sounds.

The passage behind the drum of the ear, is called the vestibulum, being the entrance to two other cavities, called the labyrinth, and the second cochlea, from its resemblance to a snail shell.

482. The principal organs of the sense of smelling are the nostrils and olfactory nerves; the ramifications of which are distributed throughout the nostrils.

Smelling is performed by the odorous effluvia in the air, being drawn into the nostrils by inspiration, and struck with such force against the olfactory nerves, as to shake them, and occasion ideas of sweet, fœtid, sour, and aromatic.

483. The taste is that sensation which all things give to the tongue; but some consider the palate, the upper part of the roof of the mouth, to be the instrument of taste.

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