Hygienic Physiology(txt+pdf+epub+mobi电子书下载)

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I.

THE SKELETON.

"Not in the World of Light alone,Where God has built His blazing throne,Nor yet alone on earth below,With belted seas that come and go,And endless isles of sunlit greenIs all thy Maker's glory seen—Look in upon thy wondrous frame,Eternal wisdom still the same!"

HOLMES.

ANALYSIS OF THE SKELETON.

NOTE.—The following Table of 206 bones is exclusive of the 8 sesamoid bones which occur in pairs at the roots of the thumb and great toe, making 214 as given by Leidy and Draper. Gray omits the bones of the ear, and names 200 as the total number.

THE SKELETON. _ | I. THE HEAD (28 bones.) | | | Frontal Bone (forehead). | | Two Parietal Bones. | | 1. CRANIUM…………..| Two Temporal (temple) Bones. | | (8 bones.) | Sphenoid Bone. | | | Ethmoid (sieve-like bone at root of nose). | | |Occipital Bone (back and base of skull). | | | | | Two Superior Maxillary (upper jaw) Bones. | | | Inferior Maxillary (lower jaw) Bone. | | | Two Malar (cheek) Bones. | | 2. FACE……………..| Two Lachrymal Bones. | | (14 bones.) | Two Turbinated (scroll like) Bones, each | | | side of nose. | | | Two Nasal Bones (Bridge of nose). | | | Vomer (the bone between the nostrils). | | |Two Palate Bones. | | | | | Hammer. | | 3. EARS……………..| Anvil. | |_ (6 bones.) |_Stirrup. | |

II.

| 1. Uses. | 2. Composition. | 1. FORM, STRUCTURE, | 3. Structure. | ETC., OF THE BONES | 4. Growth. | | 5. Repair. THE SKELETON | |6. The Joints. | | 2. CLASSIFICATION OF | 1. The Head. |_ THE BONES. | 2. The Trunk. |_3. The Limbs. THE SKELETON.

I. FORM, STRUCTURE, ETC., OF THE BONES.

(See page 269.)

THE SKELETON, or framework of the "House we live in," is composed of about 200 bones. [Footnote: The precise number varies in different periods of life. Several which are separated in youth become united in old age. Thus five of the "false vertebrć" at the base of the spine early join in one great bone—the sacrum; while four tiny ones below it often run into a bony mass—the coccyx (Fig. 6); in the child, the sternum is composed of eight pieces, while in the adult it consists of only three. While, however, the number of the bones is uncertain, their relative length is so exact that the length of the entire skeleton, and thence the height of the man, can be obtained by measuring a single one of the principal bones. Fossil bones and those found at Pompeii have the same proportion as our own.]

USES AND FORMS OF THE BONES.—They have three principal uses: 1. To protect the delicate organs; [Footnote: An organ is a portion of the body designed for a particular use, called its function. Thus the heart circulates the blood; the liver produces the bile.] 2. To serve as levers on which the muscles may act to produce motion; and 3. To preserve the shape of the body.

Bones differ in form according to the uses they subserve. For convenience in walking, some are long; for strength and compactness, some are short and thick; for covering a cavity, some are flat; and for special purposes, some are irregular. The general form is such as to combine strength and lightness. For example, all the long bones of the limbs are round and hollow, thus giving with the same weight a greater strength, [Footnote: Cut a sheet of foolscap in two pieces. Roll one half into a compact cylinder, and fold the other into a close, flat strip; support the ends of each and hang weights in the middle until they bend. The superior strength of the roll will astonish one unfamiliar with this mechanical principle. In a rod, the particles break in succession, first those on the outside, and later those in the center. In a tube, the particles are all arranged where they resist the first strain. Iron pillars are therefore cast hollow. Stalks of grass and grain are so light as to bend before a breath of wind, yet are stiff enough to sustain their load of seed. Bone has been found by experiment to possess twice the resisting property of solid oak.] and also a larger surface for the attachment of the muscles.

The Composition of the Bones at maturity is about one part animal to two parts mineral matter. The proportion varies with the age. In youth it is nearly half and half, while in old age the mineral is greatly in excess. By soaking a bone in weak muriatic acid, and thus dissolving the mineral matter, its shape will not change, but its stiffness will disappear, leaving a tough, gristly substance [Footnote: Mix a wineglass of muriatic acid with a pint of water, and place in it a sheep's rib. In a day or two, the bone will become so soft that it can be tied into a knot. In the same way, an egg may be made so pliable that it can be crowded into a narrow- necked bottle, within which it will expand, and become an object of great curiosity to the uninitiated. By boiling bones at a high temperature, the animal matter separates in the form of gelatine. Dogs and cats extract the animal matter from the bones they eat. Fossil bones deposited in the ground during the Geologic period, were found by Cuvier to contain considerable animal matter. Gelatine was actually extracted from the Cambridge mastodon, and made into glue. A tolerably nutritious food might thus be manufactured from bones older than man himself.] (cartilage) which can be bent like rubber.

If the bone be burned in the fire, thus consuming the animal matter, the shape will still be the same, but it will have lost its tenacity, and the beautiful, pure-white residue [Footnote: From bones thus calcined, the phosphorus of the chemist is made. See Steele's "Popular Chemistry," page 114. If the animal matter be not consumed, but only charred, the bone will be black and brittle. In this way, the "boneblack" of commerce is manufactured.] may be crumbled into powder with the fingers.

FIG. 2.

[Illustration: The Thigh Bone, or Femur, sawed lengthwise.]

We thus see that a bone receives hardness and rigidity from its mineral, and tenacity and elasticity from its animal matter.

The entire bone is at first composed of cartilage, which gradually ossifies or turns to bone. [Footnote: The ossification of the bones on the sides and upper part of the skull, for example, begins by a rounded spot in the middle of each one. From this spot the ossification extends outward in every direction, thus gradually approaching the edges of the bone. When two adjacent bones meet, there will be a line where their edges are in contact with each other, but have not yet united; but when more than two bones meet in this way, there will be an empty space between them at their point of junction. Thus, if you lay down three coins upon the table with their edges touching one another, there will be a three-sided space in the middle between them; if you lay down four coins in the same manner, the space between them will be four-sided. Now at the back part of the head there is a spot where three bones come together in this way, leaving a small, three-sided opening between them: this is called the "posterior fontanelle." On the top of the head, four bones come together, leaving between them a large, four-sided opening: this is called the "anterior fontanelle." These openings are termed the fontanelles, because we can feel the pulsations of the brain through them, like the bubbling of water in a fountain. They gradually diminish in size, owing to the growth of the bony parts around them, and are completely closed at the age of four years after birth.—DALTON.] Certain portions near the joints are long delayed in this process, and by their elasticity assist in breaking the shock of a fall. [Footnote: Frogs and toads, which move by jumping, and consequently receive so many jars, retain these unossified portions (epiphyses) nearly through, life, while alligators and turtles whose position is sprawling, and whose motions are measured do not have them at all—LEIDY] Hence the bones of children are tough, are not readily fractured, and when broken easily heal again; [Footnote: This is only one of the many illustrations of the Infinite care that watches over helpless infancy, until knowledge and ability are acquired to meet the perils of life.] while those of elderly people are liable to fracture, and do not quickly unite.

FIG. 3.

[Illustration: A thin slice of Bone, highly magnified showing the lacunć, the tiny tubes (canaliculi) radiating from them, and four Haversian canals, three seen crosswise and one lengthwise.]

THE STRUCTURE OF THE BONES—When a bone is sawed lengthwise, it is found to be a compact shell filled with a spongy substance This filling increases in quantity, and becomes more porous at the ends of the bone, thus giving greater size to form a strong joint, while the solid portion increases near the middle, where strength alone is needed. Each fiber of this bulky material diminishes the shock of a sudden blow, and also acts as a beam to brace the exterior wall. The recumbent position of the alligator protects him from falls, and therefore his bones contain very little spongy substance.

In the body, bones are not the dry, dead, blanched things they commonly seem to be, but are moist, living, pinkish structures, covered with a tough membrane, called the per-i-os'-te-um [Footnote: The relations of the periosteum to the bone are very interesting. Instances are on record where the bone has been removed, leaving the periosteum, from which the entire bone was afterward renewed.] (peri, around, and osteon, a bone), while the hollow is filled with marrow, rich in fat, and full of blood vessels. If we examine a thin slice with the microscope, we shall see black spots with lines running in all directions, and looking very like minute insects. These are really little cavities, called la-cu'-nć [Footnote: When the bone is dry, the lacunć are filled with air, which refracts the light, so that none of it reaches the eye, and hence the cavities appear black.] from which radiate tiny tubes. The lacunć are arranged in circles around larger tubes, termed from their discoverer, Haversian canals, which serve as passages for the blood vessels that nourish the bone.

GROWTH OF THE BONES.—By means of this system of canals, the blood circulates as freely through the bones as through any part of the body, The whole structure is constantly but slowly changing, [Footnote: Bone is sometimes produced with surprising rapidity. The great Irish Elk is calculated by Prof. Owen to have cast off and renewed, annually in its antlers eighty pounds of bone.] old material being taken out and new put in. A curious illustration is seen in the fact that if madder be mixed with the food of pigs, it will tinge their bones red.

REPAIR OF THE BONES.—When a bone is broken, the blood at once oozes out of the fractured ends. This soon gives place to a watery fluid, which in a fortnight thickens to a gristly substance, strong enough to hold them in place. Bone matter is then slowly deposited, which in five or six weeks will unite the broken parts. Nature, at first, apparently endeavors to remedy the weakness of the material by excess in the quantity, and so the new portion is larger than the old. But the extra matter will be gradually absorbed, sometimes so perfectly as to leave no trace of the injury. (See p. 271.)

A broken limb should be held in place by splints, or a plaster cast, to enable this process to go on uninterruptedly, and also lest a sudden jar might rupture the partially mended break. For a long time, the new portion consists largely of animal matter, and so is tender and pliable. The utmost care is therefore necessary to prevent a malformation.

THE JOINTS are packed with a soft, smooth cartilage, or gristle, which fits so perfectly as to be airtight. Upon convex surfaces, it is thickest at the middle, and upon concave surfaces, it is thickest at the edge, or where the wear is greatest. In addition, the ends of the bones are covered with a thin membrane, the synovial (sun, with; ovum, an egg), which secretes a viscid fluid, not unlike the white of an egg. This lubricates the joints, and prevents the noise and wear of friction. The body is the only machine that oils itself.

The bones which form the joint are tied with stout ligaments (ligo, I bind), or bands, of a smooth, silvery white tissue, [Footnote: The general term tissue is applied to the various textures of which the organs are composed. For example, the osseous tissue forms the bones; the fibrous tissue, the skin, tendons, and ligaments.] so strong that the bones are sometimes broken without injuring the fastenings.

II. CLASSIFICATION OF THE BONES.

For convenience, the bones of the skeleton are considered in three divisions: the head, the trunk, and the limbs.

1. THE HEAD.

THE BONES OF THE SKULL AND THE FACE form a cavity for the protection of the brain and the four organs of sense, viz.: sight, smell, taste, and hearing. All these bones are immovable except the lower jaw, which is hinged [Footnote: A ring of cartilage is inserted in its joints, something after the manner of a washer in machinery. This follows the movements of the jaw, and admits of freer motion, while it guards against dislocation.] at the back so as to allow for the opening and shutting of the mouth.

THE SKULL is composed, in general, of two compact plates, with a spongy layer between. These are in several pieces, the outer ones being joined by notched edges, sutures (su'tyurs,), in the way carpenters term dovetailing. (See Fig. 4.)

FIG. 4.

[Illustration: The Skull.—1. frontal bone; 2, parietal bone; 3, temporal bone; 4, the sphenoid bone; 5, ethmoid bone; 6, superior maxillary (upper jaw) bone; 7, malar bone; 8, lachrymal bone; 9, nasal bone; 10, inferior maxillary (lower jaw) bone.]

The peculiar structure and form of the skull afford a perfect shelter for the brain—an organ so delicate that, if unprotected, an ordinary blow would destroy it. Its oval or egg shape adapts it to resist pressure. The smaller and stronger end is in front, where the danger is greatest. Projections before and behind shield the less protected parts. The hard plates are not easy to penetrate. [Footnote: Instances have been known where bullets, striking against the skull, have glanced off, been flattened, or even split into halves. In the Peninsular Campaign, the author saw a man who had been struck in the forehead by a bullet which, instead of penetrating the brain, had followed the skull around to the back of the head, and there passed out.] The spongy packing deadens every blow. [Footnote: An experiment resembling the familiar one of the balls in Natural Philosophy ("Steele's Popular Physics," Fig. 6, p. 26), beautifully illustrates this point. Several balls of ivory are suspended by cords, as in Fig. 5. If A be raised and then let fall, it will transmit the force to B, and that to C, and so on until F is reached, which will fly off with the impulse. If now a ball of spongy bone be substituted for an ivory one anywhere in the line, the force will be checked, and the last ball will not stir.] The separate pieces with their curious joinings disperse any jar which one may receive, and also prevent fractures from spreading.

FIG. 5.

[Illustration]

The frequent openings in this strong bone box afford safe avenues for the passage of numerous nerves and vessels which communicate between the brain and the rest of the body.

FIG. 6.

[Illustration: The Spine; the seven vertebrć of the neck, cervical; the twelve of the back, dorsal; the five of the loins, lumbar; a, the sacrum, and b, the coccyx, coming the nine "false vertebrć." (p. 3).]

2 THE TRUNK.

THE TRUNK has two important cavities. The upper part, or chest, contains the heart and the lungs, and the lower part, or abdomen, holds the stomach, liver, kidneys, and other organs (Fig. 31). The principal bones are those of the spine, the ribs, and the hips.

THE SPINE consists of twenty-four bones, between which are placed pads of cartilage. [Footnote: These pads vary in thickness from one fourth to one half an inch. They become condensed by the weight they bear during the day, so that we are somewhat shorter at evening than in the morning. Their elasticity causes them to resume their usual size during the night, or when we lie down for a time.] A canal is hollowed out of the column for the safe passage of the spinal cord. (See Fig. 50.) Projections (processes) at the back and on either side are abundant for the attachment of the muscles. The packing acts as a cushion to prevent any jar from reaching the brain when we jump or run, while the double curve of the spine also tends to disperse the force of a fall. Thus on every side the utmost caution is taken to guard that precious gem in its casket.

THE PERFECTION OF THE SPINE surpasses all human contrivances. Its various uses seem a bundle of contradictions. A chain of twenty-four bones is made so stiff that it will bear a heavy burden, and so flexible that it will bend like rubber; yet, all the while, it transmits no shock, and even hides a delicate nerve within that would thrill with the slightest touch. Resting upon it, the brain is borne without a tremor; and, clinging to it, the vital organs are carried without fear of harm.

FIG. 7.

[Illustration: B, the first cervical vertebra, the atlas; A, the atlas, and the second cervical vertebra, the axis; e, the odontoid process; c, the foramen.]

THE SKULL ARTICULATES with (is jointed to) the spine in a peculiar manner. On the top of the upper vertebra (atlas [Footnote: Thus called because, as, in ancient fable, the god Atlas supported the world on his shoulders, so in the body this bone bears the head.]) are two little hollows (a, b, Fig. 7), nicely packed and lined with the synovial membrane, into which fit the corresponding projections on the lower part of the skull, and thus the head can rock to and fro. The second vertebra (axis) has a peg, e, which projects through a hole, c, in the first.

FIG. 8.

[Illustration: The Thorax or Chest. a, the sternum; b to c, the true ribs; d to h, the false ribs; g, h, the floating ribs; i, k, the dorsal vertebrć.]

The surfaces of both vertebrć are so smooth that they easily glide on each other, and thus, when we move the head side wise, the atlas turns around the peg, e, of the axis.

THE RIBS, also twenty-four in number, are arranged in pairs on each side of the chest. At the back, they are all attached to the spine. In front, the upper seven pairs are tied by cartilages to the breastbone (sternum); three are fastened to each other and to the cartilage above, and two, the floating ribs, are loose.

The natural form of the chest is that of a cone diminishing upward. But, owing to the tightness of the clothing commonly worn, the reverse is often the case. The long, slender ribs give lightness, [Footnote: If the chest wall were in one bone thick enough to resist a blow, it would be unwieldy and heavy As it is, the separate bones bound by cartilages yield gradually, and diffuse the force among them all, and so are rarely broken.] the arched form confers strength, and the cartilages impart elasticity,—properties essential to the protection of the delicate organs within, and to freedom of motion in respiration. (See note, p. 80.)

FIG. 9.

[Illustration: The Pelvis. a, the sacrum; b, b, the right and the left innominatum.]

THE HIP BONES, called by anatomists the innominata, or nameless bones, form an irregular basin styled the pelvis (pelvis, a basin). In the upper part, is the foot of the spinal column—a wedge-shaped bone termed the sacrum [Footnote: So called because it was anciently offered in sacrifice.] (sacred), firmly planted here between the

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