Physiology and Hygiene for Secondary Schools | Page 9

Life.*--The preservation of any cell group in its
natural condition, whether it be plant or animal, is accomplished
through keeping it alive. If life ceases, the group quickly disintegrates
and its elements become scattered, a fact which is verified through
everyday observation. Though the nature of life is unknown, it may be
looked upon as the organizer and preserver of the protoplasm. But in
preserving the protoplasm it also preserves the entire cell group, or
body. Life is thus the most essential condition of the body. With life all
portions of the body are concerned, and toward its maintenance all the
activities of the body organization are directed.
*The Nutrient Fluid in its Relations to the Cells.*--The maintenance of
life within the cells requires, as we have seen, that they be supplied
with water, food, and oxygen, and that they be relieved of such wastes
as they form. This double purpose is accomplished through the agency
of an internal nutrient fluid, a portion of which has already been
referred to as the lymph. Not only does this fluid supply the means for
keeping the cells alive, but, through the cells, it is also the means of
preserving the life of the body as a whole.
The cells, however, rapidly exhaust the nutrient fluid. They take from it
food and oxygen and they put into it their wastes. To prevent its
becoming unfit for supplying their needs, food and oxygen must be
continually added to this fluid, and waste materials must be continually
removed. This is not an easy task. As a matter of fact, the preparation,
distribution, and purification of the nutrient fluid requires the direct or

indirect aid of practically all parts of the body. It supplies for this
reason a broad basis for the division of labor on the part of the cells.
*Relation of the Body to its Environment.*--While life is directly
dependent upon the internal nutrient fluid, it is indirectly dependent
upon the physical surroundings of the body. Herein lies the need of the
external organs--the feet and legs for moving about, the hands for
handling things, the eyes for directing movements, etc. That the great
needs of the body are supplied from its surroundings are facts of
common experience. Food, shelter, air, clothing, water, and the means
of protection are external to the body and form a part of its environment.
In making the things about him contribute to his needs, man encounters
a problem which taxes all his powers. Only by toil and hardship, "by
the sweat of his brow," has he been able to wrest from his surroundings
the means of his sustenance.
*The Main Physiological Problems.*--The study of the body is thus
seen to resolve itself naturally into the consideration of two main
problems:
1. That of maintaining in the body a nutrient fluid for the cells.
2. That of bringing the body into such relations with its surroundings
as will enable it to secure materials for the nutrient fluid and satisfy its
other needs.
The first problem is internal and includes the so-called vital processes,
known as digestion, circulation, respiration, and excretion. The second
problem is external, as it were, and includes the work of the external
organs--the organs of motion and of locomotion and the organs of
special sense. These problems are closely related, since they are the two
divisions of the one problem of maintaining life. Neither can be
considered independently of the other. In the chapter following is taken
up the first of these problems.
*Summary.*--The individual parts, or units, that form the body
organization are known as cells. These consist of minute but definitely
arranged portions of protoplasm and are held together by the

intercellular material. They build up the body and carry on its different
activities. The tissues are groups of like cells. By certain general
activities the cells maintain their existence in the tissues and by the
exercise of certain special activities they adapt the tissues to their
purposes in the body. The body, as a cell organization, has its activities
directed under normal conditions toward a single purpose--that of
maintaining life. In the accomplishment of this purpose a nutrient fluid
is provided for the cells and proper relations between the body and its
surroundings are established.
*Exercises.*--1. If a tissue be compared to a brick wall, to what do the
separate bricks correspond? To what the mortar between the bricks?
2. Draw an outline of a typical cell, locating and naming the main
divisions.
3. How do the cells enable the body to grow? Describe the process of
cell-division.
4. How does the general work of cells differ from their special work?
Define absorption, excretion, and assimilation as applied to the cells.
5. Compare the conditions surrounding a one-celled animal, living in
water, to the conditions