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Table of Contents

The Bones—Their Form and Composition—The Properties of Bone—The Skeleton—The Joints—The Spinal Column—The Growth of Bone—The Repair of Bone.

1. The framework of the body? The superstructure? Softness and delicacy of the organs? How protected?

1. The Bones.—The framework which sustains the human body is composed of the Bones. The superstructure consists of the various organs on which the processes of life depend. These organs are soft and delicately formed, and, if unprotected, would, in most cases, rapidly be destroyed when subjected to violence, however slight. The bones, having great strength and power of resistance, afford the protection required.

2. The more delicate the organ? Example in relation to the brain? The eye? The lungs? The services performed by the bones?

2. The more delicate the organ, the more completely does Nature shield it. For example: the brain, which is soft in structure, is enclosed on all sides by a complete box of bone; the eye, though it must be near the surface of the body to command an extensive view, is sheltered from injury within a deep recess of bone; the lungs, requiring freedom of motion as well as protection, are surrounded by a large case of bone and muscle. The bones serve other useful purposes. They give permanence of form to the body, by holding the softer parts in their proper places. They assist in movement, by affording points of attachment to those organs which have power of motion—the muscles.

3. Their shape and size? Of what composed? Possibility of being separated? Effect of fire? Of dilute acid?

3. The Form and Composition of the Bones.—Their shape and size vary greatly in different parts of the body, but generally they are arranged in pairs, one bone for each side of the body. They are composed of both mineral and animal substances, united in the proportion of two parts of the former to one of the latter; and we may separate each of these substances from the other for examination. First, if we expose a bone to the action of fire, the animal substance is driven off, or "burned out." We now find that, though the shape of the bone is perfectly retained, what is left is no longer tough, and does not sustain weight as before. Again, we may remove the mineral portion, which is a form of lime, by placing a bone into a dilute acid. The lime will be dissolved out, and the shape of the bone remain as before; but now its firmness has disappeared, and it may be bent without breaking.

4. Effect of deficiency of ingredient? Usefulness of the lime? Of the animal substance? Effect of their union? Condition, in youth? Old age?

4. If, for any reason, either of these ingredients is disproportionate in the bone during life, the body is in danger. The lime is useful in giving rigidity of form, while the animal substance insures toughness and elasticity. By their union, we are able to withstand greater shocks and heavier falls than would be possible with either alone. In youth, the period of greatest activity, the animal constituent is in excess: a bone then does not break so readily, but, when broken, unites with great rapidity and strength. On the other hand, the bones of old persons are more easily broken, and in some cases fail to unite. The mineral matter being then in excess, indicates that the period of active exertion is drawing to a close.

Fig. 1.—Section of Bone.

Fig. 2.

Structure of bone enlarged.

5. In what respect admirably fashioned? Its formation? Microscopic examination? The inference? "Line of beauty?"

5. The Structure of the Bones.—If we examine one of the long bones, which has been sawn through lengthwise, we observe that it is admirably fashioned for affording lightness as well as strength (Fig. 1). Its exterior is hard and resisting, but it is porous at the broad extremities, while through the central portion there is a cavity or canal which contains an oily substance, called marrow. Let us now take a thin section of bone, and examine it under the microscope; we discover that it is pierced by numerous fine tubes (Fig. 2), about which layers of bone-substance are arranged. Accordingly, though a bone be as hard as stone externally, it is by no means as heavy as stone, by reason of its light interior texture. Another element of power is found in the curved outline of the bones. The curved line is said to be "the line of beauty," as it certainly is the line of strength, and is uniformly employed in the bones whose position exposes them to accident.

Fig. 3.—The Skeleton

6. Number of bones? Skeleton? The skull? Chest? The trunk? The trunk and skull, how maintained? What of the arms? Legs?

6. The Skeleton.—The number of bones in the human body exceeds two hundred. When these are joined together in the proper places, they form what is termed the Skeleton (Fig. 3). It embraces three important cavities. The first, surmounting the frame, is a box of bone, called the skull; below this, is a bony case, or "chest;" and lower down is a bony basin, called the pelvis. The two latter compose the trunk. The trunk and skull are maintained in their proper relations by the "spinal column." Branching from the trunk are two sets of limbs: the arms, which are attached to the chest by means of the "collar-bone" and "shoulder-blade;" and the legs, directly joined to the lower part of the trunk.

7. Design of the cavities? Give the examples.

7. The cavities of which we have spoken, are designed for the lodgment and protection of the more delicate and perishable parts of the system. Thus, the skull, together with the bones of the face, shelters the brain and the organs of four senses—sight, hearing, smell, and taste. The chest contains the heart, lungs, and great blood-vessels, while the lower part of the trunk sustains the liver, stomach, and other organs.

8. Joint or articulation? Movable joints, how compacted? The ligaments of the movable joints? What is a sprain? Consequence of a serious sprain?

8. The Joints.—The point of union of two or more bones forms a joint or articulation, the connection being made in various ways according to the kind and amount of motion desired. The movable joints are compacted together by certain strong fibrous bands, called ligaments. These ligaments are of a shining, silvery whiteness, and very unyielding; so much so, that when sudden violence is brought to bear in the vicinity of a joint, the bone to which a ligament is attached may be broken, while the ligament itself remains uninjured. When this connecting material of the joints is strained or lacerated by an accident, a "sprain" is the consequence. An injury of this sort may be, and frequently is, quite as serious as the breaking of a bone.

Fig. 4.—Cells of Cartilage.

9. Office of the ligament? What must it have? How accomplished? Describe it. Synovia?

9. The ligament, then, secures firmness to the joint; it must also have flexibility and smoothness of motion. This is accomplished by a beautiful mechanism the perfection of which is only feebly imitated by the most ingenious contrivance of man. The ends of the bones are covered by a thin layer of cartilage, which being smooth and elastic, renders all the movements of the joint very easy. In addition to this, there is an arrangement introduced for "lubricating" the joint, by means of a delicate sac containing fluid. This fluid is constantly supplied in small quantities, but only so fast as it is used up in exercise. In appearance, it is not unlike the white of an egg, and hence its name synovia, or egg-like.

10. What do we observe as regards the composition of a joint? The ligament and cartilage? What varies? Example of the skull? Other examples? The ball-and-socket joint?

10. Thus, we observe, that two very different substances enter into the composition of a joint. The ligament, very unyielding, affords strength, while the cartilage, elastic and moist, gives ease and smoothness of motion. The amount of motion provided for varies greatly in different joints. In some there is none at all, as in the skull, where one bone is dove-tailed into another by what are termed sutures. Others have a hinge-like motion, such as those of the elbow, wrist, ankle, and knee; the most complete of these being the elbow-joint (Fig. 5). Belonging to another class, the ball-and-socket joint, is that at the shoulder, possessing a freedom of motion greater than any other in the body.

Fig. 5.—Elbow Joint. A, Bone of the arm; B, C, Bones of the fore-arm.

11. What is the spinal column? What does it connect and form? Joints of the vertebræ? Amount of motion? Result?

11. The Spinal Column.—The spinal column is often spoken of as the "back-bone," as if it were a single bone, while, in reality, it is composed of a chain of twenty-six small bones, called vertebræ. The spinal column is a wonderful piece of mechanism. It not only connects the important cavities of the body, as has already been shown, but, also, itself forms a canal, which contains the spinal cord. The joints of the vertebræ are remarkable for the thick layers of cartilage which separate the adjacent surfaces of bone. The amount of motion between any two of these bones is not great; but these little movements, taken together, admit of very considerable flexibility, in several directions, without endangering the supporting power of the column.

12. Elasticity of the frame? Protection of the brain from shocks? Tallness of persons? Effects of reclining?

Fig. 6—The Spinal Column.

12. The abundant supply of intervertebral cartilage has another important use, namely, it adds greatly to the elasticity of the frame. It is due, in part, to this elastic material, and in part to the frequent curves of the spine, that the brain and other delicate organs are protected from the shock of sudden falls or jars. During the day, the constant pressure upon these joints, while the body is erect, diminishes the thickness of the cartilages; so that a person is not so tall in the evening as in the morning. The effects of this compression pass away when the body reclines in a horizontal position.

13. Change in bone? Example—animal and madder. Rapidity of change in color? Waste and repair?

13. The Growth of Bone.—Bone, like all the other tissues of the body, is constantly undergoing change, old material being withdrawn, and new particles taking their place. This has been shown conclusively by experiments. If an animal be fed with madder—a red coloring matter—for a day or two, the bones soon become tinged; then, if the madder be discontinued for a few days, the original color returns. If, however, this material be alternately given and withheld, at short intervals, the bone will be marked by a succession of red and white rings. In very young animals, all the bones become colored in a single day; in older ones, a longer time is required. The process of waste and repair, therefore, is constantly taking place in this hard substance, and with astonishing rapidity.

14. The Repair of Bone.—Nature's provision for uniting broken bones is very complete. At first, blood is poured out around the ends of the bone, as a result of the injury. This is gradually absorbed, and gives place to a watery fluid, which, thickening from day to day, acquires, at the end of two weeks, the consistency of jelly. This begins to harden, by a deposit of new bone-substance, until, at the expiration of five or six weeks, the broken bone may be said to be united. It is, however, still fragile, and must be used carefully a few weeks longer. The process of hardening continues, and months must pass before the union can be said to be complete.

QUESTIONS FOR TOPICAL REVIEW.

	PAGE
1. What useful purposes do the bones serve?	15, 16
2. State what you can of the composition of the bones.	16
3. Of the usefulness of lime in the bones.	16
4. Of the usefulness of animal substance in the bones.	16
5. State what you can of the structure of the bones.	17
6. Of the strength belonging to the bones.	15, 16, 17
7. What is meant by the human skeleton?	19
8. Give a description of its construction.	19
9. What is meant by a joint in the human frame?	19
10. State what you can of the movable joints.	19, 20
11. What office is performed by the ligaments of the joints?	19, 20
12. What by the cartilage at the joints?	20
13. What movable joints are there?	20, 21
14. Describe the construction of the spinal column.	21
15. What properties and powers does the spinal column possess?	21, 22
16. When is a person taller than at other times?	22
17. Give the reason for this.	22
18. What can you state of the growth of bone?	22
19. Describe the process by which a broken bone is repaired.	23

Fig. 7.—The Muscles.

CHAPTER II.