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Page 10
Several of the organs of the body, in addition to the formation of
secretions which are discharged on the surfaces by means of their
ducts, produce also substances which pass directly into the blood or
lymph, and have an influence in stimulating or otherwise regulating
the activity of other organs. There are also certain organs of
glandular structure which are called the _ductless glands_; these
are not connected with the surface and all their secretion passes into
the blood. It is a part of recent knowledge that the substances
produced in these glands are of great importance for the body, some of
them even essential for the maintenance of life. In front of the neck
is such an organ, the thyroid gland (Fig. 8, 14). Imperfect
development or absence of this organ, or an inactive condition of it,
produces in the child arrested growth and deficient mental development
known as cretinism, and in the adult the same condition gives rise to
mental deterioration, swelling of the skin, due to a greater content
of water, and loss of hair. This deficiency in the production of
thyroid secretion can be made good and the symptoms removed by feeding
the patient with similar glands removed from animals. The very complex
disease known as exophthalmic goitre, and shown by irregular and rapid
action of the heart, protruding eyeballs and a variety of mental
symptoms, is also associated with this gland, and occasioned not by a
deficiency but by an excess or perversion of its secretion.
Adjoining the thyroid there are four small glands, the parathyroids,
each about the size of a split pea. The removal of these glands in
animals produces a condition resembling acute poisoning accompanied by
spasmodic contraction of the muscles. A small glandular organ at the
base of the brain, the pituitary body, produces a secretion, one of
the most marked properties of which is a control of growth,
particularly that of the bones. Most cases of giantism, combined as
they are with imperfect mentality, are due to disease of this gland.
There are glands near the kidney which regulate the pressure of the
blood in the arteries by causing contraction of their muscular walls.
The sexual characteristics in the male and female are due to an
internal secretion produced by the respective sexual glands which
affects growth, body development and mentality.
So is the body constituted. A series of surfaces, all connected, of
enormous size, which enclose a large number of organs and tissues, the
activities of which differ, but all are co�rdinated to serve the
purposes of the organism as a whole. We should think of the body not
as an assemblage of more or less independent entities, but as a single
organism in which all parts are firmly knit together both in structure
and in function, as are the components of a single cell.
FOOTNOTES:
[1] They do, however, take place, since within comparatively
few years whole species have completely disappeared; for example, the
great auk and the passenger pigeon. In these cases it is not known
what part disease played in the destruction.
[2] A tissue represents an aggregate of similar cells with
the intercellular substances in relation with these as connective
tissue, muscular tissue, etc. Where such cell aggregates are localized
and where the cells are arranged in structures having definite form
and size and performing a definite function, it is customary to
designate such structures as organs, as the brain, liver, etc.
CHAPTER II
NO SHARP LINE OF DEMARKATION BETWEEN HEALTH AND DISEASE.--THE
FUNCTIONAL NUTRITIVE AND FORMATIVE ACTIVITIES OF CELLS.--DESTRUCTION
AND REPAIR CONSTANT PROCESSES IN LIVING MATTER.--INJURIES TO THE
BODY.--THE EFFECT OF HEAT.--THE ACTION OF POISONS.--THE LESIONS OF
DISEASE.--REPAIR.--THE LAWS GOVERNING REPAIR.--RELATION OF REPAIR TO
COMPLEXITY OF STRUCTURE AND AGE.--THE RESERVE FORCE OF THE BODY.--
COMPENSATORY PROCESSES IN THE BODY.--OLD AGE.--THE DIMINUTION OF
RESISTANCE TO THE EFFECT OF THE ENVIRONMENT A PROMINENT FACTOR IN OLD
AGE.--DEATH.--HOW BROUGHT ABOUT.--CHANGES IN THE BODY AFTER DEATH.--
THE RECOGNITION OF DEATH.
There is no sharp line separating health from disease; changes in the
tissues of the same nature, or closely akin to those which are found
in disease, are constantly occurring in a state of health. The
importance of parasites in causing disease has led to the conception
of disease as almost synonymous with parasitism; but it must be
remembered that the presence of parasites living at the expense of the
body is perfectly consistent with a state of health. Degeneration,
decay and parasitism only become disease factors when the conditions
produced by them interfere with the life which is the normal or usual
for the individual concerned.
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