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Page 8
Between these various surfaces is the real interior of the body, in
which there are many sorts of living tissues,[2] each, of which, in
addition to maintaining itself, has some function necessary for the
maintenance of the body as a whole. Many of these tissues have for
their main purpose the adjustment and co�rdination of the activities
of the different organs to the needs of the organism as a whole. The
activity of certain of the organs is essential for the maintenance of
life; without others life can exist for a time only; and others, such
as the genital glands, while essential for the preservation of the
life of the species, are not essential for the individual. There is a
large amount of reciprocity among the tissues; in the case of paired
organs the loss of one can be made good by increased activity of the
remaining, and certain of the organs are so nearly alike in function
that a loss can be compensated for by an increase or modification of
the function of a nearly related organ. The various internal parts are
connected by means of a close meshwork of interlacing fibrils, the
connective tissue, support and strength being given by the various
bones. Everywhere enclosing all living cells and penetrating into the
densest of the tissues there is fluid. We may even consider the body
between the surfaces as a bag filled with fluid into which the various
cells and structures are packed.
[Illustration: FIG. 9.--A LONGITUDINAL SECTION THROUGH THE FEMALE
PELVIS.
1. The Fallopian tube which forms the connection between
the ovary and the uterus.
2. The ovary.
3. The body of the uterus.
4. The uterine canal.
5. The urinary bladder represented as empty.
6. The entrance of the ureter.
7. The pubic bone.
8. The urethra.
9. The vagina.
10. The common external opening or vulva.
11. The rectum and anus.]
[Illustration: FIG. 10.--THE LUNGS AND WINDPIPE. Parts of the lungs
have been removed to show the branching of the air tubes or bronchi
which pass into them. All the tubes and the surfaces of the lungs
communicate with the inner surface of the body through the larynx.]
The nervous system (Fig. 8) represents one of the most important of
the enclosed organs. It serves an important function, not only in
regulating and co�rdinating all functions, but by means of the special
senses which are a part of it, the relations of the organism as a
whole with the environment are adjusted. It consists of a large
central mass, the brain and spinal cord, which is formed in the embryo
by an infolding of the external surface, much in the same way that a
gland is formed; but the connection with the surface is lost in
further development and it becomes completely enclosed. Connected with
the central nervous mass, forming really a part of it and developing
from it, are the nerves, which appear as white fibrous cords and after
dividing and subdividing, are as extremely fine microscopic filaments
distributed to all parts of the body. By means of the nerves all
impressions are conveyed to the brain and spinal cord; all impulses
from this, whether conscious or unconscious, are conveyed to the
muscles and other parts. The brain is the sole organ of psychical
life; by means of its activity the impressions of the external world
conveyed to it through the sense organs are converted into
consciousness. Whatever consciousness is, and on this much has been
written, it proceeds from or is associated with the activity of the
brain cells just as truly as the secretion of gastric juice is due to
the activity of the cells of the stomach. The activity of the nervous
system is essential for extra-uterine life; life ceases by the
cessation of circulation and respiration when either the whole or
certain small areas of its tissue are destroyed. In intra-uterine
life, with the narrow and unchanging environment of the fluid within
the uterine cavity which encloses the foetus, life is compatible with
the absence or rudimentary development of the nervous system. The
foetus in this condition may be otherwise well developed, and it would
be not a misuse of words to say that it was healthy, since it is
adjusted to and in harmony with its narrow environment, but it would
not be normal. The intra-uterine life of the unborn child, it must be
remembered, is carried out by the transmission of energy from the
mother to the foetus by means of the close relation between the
maternal and foetal circulation. It is only when the free existence
demands activities not necessary in intra-uterine life that existence
without a central nervous system becomes impossible.
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