Chapter 2 GENERAL VIEW OF THE BODY

External Divisions.-Examined from the outside, the body presents certain parts, or divisions, familiar to all. The main, or central, portion is known as the trunk, and to this are attached the head, the upper extremities, and the lower extremities. These in turn present smaller divisions which are also familiar. The upper part of the trunk is known as the thorax, or chest, and the lower part as the abdomen.

The portions of the trunk to which the arms are attached are the shoulders, and those to which the legs are joined are the hips, while the central rear portion between the neck and the hips is the back. The fingers, the hand, the wrist, the forearm, the elbow, and the upper arm are the main divisions of each of the upper extremities. The toes, the foot, the ankle, the lower leg, the knee, and the thigh are the chief divisions of each of the lower extremities. The head, which is joined to the trunk by the neck, has such interesting parts as the eyes, the ears, the nose, the jaws, the cheeks, and the mouth. The entire body is inclosed in a double covering, called the skin, which protects it in various ways.

The Tissues.-After examining the external features of the body, we naturally inquire about its internal structures. These are not so easily investigated, and much which is of interest to advanced students must be omitted from an elementary course. We may, however, as a first step in this study, determine what kinds of materials enter into [pg 005]the construction of the body. For this purpose the body of some small animal should be dissected and studied. (See observation at close of chapter.) The different materials found by such a dissection correspond closely to the substances, called tissues, which make up the human body. The main tissues of the body, as ordinarily named, are the muscular tissue, the osseous tissue, the connective tissue, the nervous tissue, the adipose tissue, the cartilaginous tissue, and the epithelial and glandular tissue. Most of these present different varieties, making all together some fifteen different kinds of tissues that enter into the construction of the body.2

General Purposes of the Tissues.-The tissues, first of all, form the body. As a house is constructed of wood, stone, plaster, iron, and other building materials, so is the body made up of its various tissues. For this reason the tissues have been called the building materials of the body.

In addition to forming the body, the tissues supply the means through which its work is carried on. They are thus the working materials of the body. In serving this purpose the tissues play an active r?le. All of them must perform the activities of growth and repair, and certain ones (the so-called active tissues) must do work which benefits the body as a whole.

Purposes of the Different Tissues.-In the construction of the body and also in the work which it carries on, the different tissues are made to serve different purposes. The osseous tissue is the chief substance in the bony framework, or skeleton, while the muscular tissue produces the different movements of the body. The connective[pg 006] tissue, which is everywhere abundant, serves the general purpose of connecting the different parts together. Cartilaginous tissue forms smooth coverings over the ends of the bones and, in addition to this, supplies the necessary stiffness in organs like the larynx and the ear. The nervous tissue controls the body and brings it into proper relations with its surroundings, while the epithelial tissue (found upon the body surfaces and in the glands) supplies it with protective coverings and secretes liquids. The adipose tissue (fat) prevents the too rapid escape of heat from the body, supplies it with nourishment in time of need, and forms soft pads for delicate organs like the eyeball.

Properties of the Tissues.-If we inquire how the tissues are able to serve such widely different purposes, we find this answer. The tissues differ from one another both in composition and in structure and, on this account, differ in their properties.3 Their different properties enable them to serve different purposes in the body. Somewhat as glass is adapted by its transparency, hardness, and toughness to the use made of it in windows, the special properties of the tissues adapt them to the kinds of service which they perform. Properties that adapt tissues to their work in the body are called essential properties. The most important of these essential properties are as follows:

1. Of osseous tissue, hardness, stiffness, and toughness. 2. Of muscular tissue, contractility and irritability. 3. Of nervous tissue, irritability and conductivity. 4. Of cartilaginous tissue, stiffness and elasticity. 5. Of connective tissue, toughness and pliability. 6. Of epithelial tissue, ability to resist the action of external forces and power to secrete.

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Fig. 1-Hand and forearm, showing the grouping of muscular and connective tissues in the organ for grasping.

Tissue Groups.-In the construction of the body the tissues are grouped together to form its various divisions or parts. A group of tissues which serves some special purpose is known as an organ. The hand, for example, is an organ for grasping (Fig. 1). While the different organs of the body do not always contain the same tissues, and never contain them in the same proportions, they do contain such tissues as their work requires and these have a special arrangement-one adapted to the work which the organs perform.

In addition to forming the organs, the tissues are also grouped in such a manner as to provide supports for organs and to form cavities in which organs are placed. The various cavities of the body are of particular interest and importance. The three largest ones are the cranial cavity, containing the brain; the thoracic cavity, containing the heart and the lungs; and the abdominal cavity, containing the stomach, the liver, the intestines, and other important organs (Fig. 2). Smaller cavities serving different purposes are also found.

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Fig. 2-Diagram of a lengthwise section of the body to show its large cavities and the organs which they contain.

Organs and Systems.-The work of the body is carried on by its various organs. Many, in fact the majority, of these organs serve more than one purpose. The tongue[pg 009] is used in talking, in masticating the food, and in swallowing. The nose serves at least three distinct purposes. The mouth, the arms, the hands, the feet, the legs, the liver, the lungs, and the stomach are also organs that serve more than one purpose. This introduces the principle of economy into the construction of the body and diminishes the number of organs that would otherwise be required.

The various organs also combine with one another in carrying on the work of the body. An illustration of this is seen in the digestion of the food-a process which requires the combined action of the mouth, stomach, liver, intestines, and other organs. A number of organs working together for the same purpose form a system. The chief systems of the body are the digestive system, the circulatory system, the respiratory system, the muscular system, and the nervous system.

The Organ and its Work.-A most interesting question relating to the work of the organ is this: Does the organ work for its own benefit or for the benefit of the body as a whole? Does the hand, for example, grasp for itself or in order that the entire body may come into possession? Only slight study is sufficient to reveal the fact that each organ performs a work which benefits the body as a whole. In other words, just as the organ itself is a part of the body, the work which it does is a part of the necessary work which the body has to do.

But in working for the general good, or for the body as a whole, each organ becomes a sharer in the benefits of the work done by every other organ. While the hand receives only a little of the nourishment contained in the food which it places in the mouth or of the heat from, fuel which it places on the fire, it is aided and supported by the work of all the other organs of the body-eyes, [pg 010] feet, brain, heart, etc. The hand does not and cannot work independently of the other organs. It is one of the partners in a very close combination where, by doing a particular work, it, shares in the profits of all. What is true of the hand is true of every other organ of the body.

An Organization.-The relations which the different organs sustain to each other and to the body as a whole suggest the possibility of classifying the body as an organization. This term is broadly applied to a variety of combinations. An organization is properly defined as any group of individuals which, in working together for a common purpose, practices the division of labor. This definition will be better understood by considering a few familiar examples.

A baseball team is an organization. The team is made up of individual players. These work together for the common purpose of winning games. They practice the division of labor in that the different players do different things-one catching, another pitching, and so on. A manufacturing establishment which employs several workmen may also be an organization. The article manufactured provides the common purpose toward which all strive; and, in the assignment of different kinds of work to the individual workmen, the principle of division of labor is carried out. For the same reason a school, a railway system, an army, and a political party are organizations.

An organization of a lower order of individuals than these human organizations is to be found in a hive of bees. This is made up of the individual bees, and these, in carrying on the general work of the hive, are known to practice the division of labor.

Is the Body an Organization?-If the body is an organization, it must fulfill the conditions of the definition. It[pg 011] must be made up of separate or individual parts. These must work together for the same general purpose, and, in the accomplishment of this purpose, must practice the division of labor. That the body practices the division of labor is seen in the related work of the different organs. That it is made up of minute, but individual, parts will be shown in the chapter following. That it carries on a general work which is accomplished through the combined action of its individual parts is revealed through an extended study of its various activities. The body is an organization. Moreover, it is one of the most complex and, at the same time, most perfect of the organizations of which we have knowledge.

Summary.-Viewed from the outside, the body is seen to be made up of divisions which are more or less familiar. Viewed internally, it is found to consist of different kinds of materials, called tissues. The tissues are adapted, by their properties, to different purposes both in the construction of the body and in carrying on its work. The working parts of the body are called organs and these in their work combine to form systems. The entire body, on account of the method of its construction and the character of its work, may be classed as an organization.

Exercises.-1. Name and locate the chief external divisions of the body.

2. What tissues may be found by dissecting the leg of a chicken?

3. Name the most important properties and the most important uses of muscular tissue, osseous tissue, and connective tissue.

4. Define an organ. Define a system. Name examples of each.

5. Name the chief cavities of the body and the organs which they contain.

6. What tissues are present in the hand? How does each of these aid in the work of the hand?

[pg 012]7. Define an organization. Show that a railway system, an army, and a school are organizations.

8. What is meant by the phrase "division of labor"? In what manner is the division of labor practiced in a shoe or watch factory? What are the advantages?

9. What are the proofs that the body is an organization?

PRACTICAL WORK

Observation on the Tissues.-Examine with care the structures in the entire leg of a chicken, squirrel, rabbit, or other small animal used for food. Observe, first of all, the external covering, consisting of cuticle and hair, claws, scales, or feathers, according to the specimen. These are similar in structure, and they form the epidermis, which is one kind of epithelial tissue. With a sharp knife lay open the skin and observe that it is attached to the parts underneath by thin, but tough, threads and sheaths. These represent a variety of connective tissue. The reddish material which forms the greater portion of the specimen is a variety of muscular tissue, and its divisions are called muscles. With a blunt instrument, separate the muscles, by tearing apart the connective tissue binding them together, and find the glistening white strips of connective tissue (tendons) which attach them to the bones. Find near the central part of the leg a soft, white cord (a nerve) which represents one variety of nervous tissue. The bones, which may now be examined, form the osseous tissue. At the ends of the bones will be found a layer of smooth, white material which represents one kind of cartilaginous tissue. The adipose, or fatty, tissue, which is found under the skin and between the other tissues, is easily recognized.

Relation of the Tissues to the Organs.-Observe in the specimen just studied the relation of the different tissues to the organ as a whole (regarding the leg as an organ), i.e., show how each of the tissues aids in the work which the organ accomplishes. Show in particular how the muscles supply the foot with motion, by tracing out the tendons that connect them with the toes. Pull on the different tendons, noting the effect upon the different parts of the foot.

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