Physiology and Hygiene for Secondary Schools | Page 4

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 rôle. 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 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.
[Fig. 1]
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.
[Fig. 2]
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 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.