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Page 21
The pain in an inflamed part is due to a number of factors, but
chiefly to the increased pressure upon the sensory nerves caused by
the exudate. The pain varies so greatly in degree and character that
parts which ordinarily have little sensation may become exquisitely
painful when inflamed. The pain is usually greater when the affected
part is dense and unyielding, as the membranes around bones and teeth.
The pain is often intermittent, there being acute paroxysms
synchronous with the pulse, this being due to momentary increase of
pressure when more blood is forced into the part at each contraction
of the heart. The pain may also be due to the direct action of an
injurious substance upon the sensory nerves, as in the case of the
sting of an insect where the pain is immediate and most intense before
the exudate has begun to appear.
When an inflamed area is examined, after twenty-four hours, by
hardening the tissue in some of the fluids used for this purpose and
cutting it into very thin slices by means of an instrument called a
microtome, the microscope shows a series of changes which were not
apparent on naked eye examination. The texture is looser, due to the
exudate which has dilated all the spaces in the tissue. Red and white
corpuscles in varying numbers and proportions infiltrate the tissue;
all the cells which belong to the part, even those forming the walls
of the vessels, are swollen, the nuclei contain more chromatin, and
the changes in the nuclei which indicate that the cells are
multiplying appear. The blood vessels are dilated, and the part in
every way gives the indication of a more active life within it. There
are also evidences of the tissue injury which has called forth all the
changes which we have considered. (Fig. 15.)
[Illustration: FIG. 15--A SECTION OF AN INFLAMED LUNG SHOWING THE
EXUDATE WITHIN THE AIR SPACES. Compare this with Fig 6. Fig 15 is from
the human lung, in which the air spaces are much larger than in the
mouse.]
The microscopic examination of any normal tissue of the body shows
within it a variable number of cells which have no intimate
association with the structure of the part and do not seem to
participate in its function. They are found in situations which
indicate that these cells have power of active independent motion. In
the inflamed tissue a greatly increased number of these cells is
found, but they do not appear until the height of the process has
passed, usually not before thirty-six or forty-eight hours after the
injury has been received. The numbers present depend much upon the
character of the agent which has produced the injury, and they may be
more numerous than the ordinary leucocytes which migrate from the
blood vessels.
All these changes which an injured part undergoes are found when
closely analyzed to be purposeful; that is, they are in accord with
the conditions under which the living matter acts, and they seem to
facilitate the operation of these conditions. It has been said that
the life of the organism depends upon the co�rdinated activity of the
living units or cells of which it is composed. The cells receive from
the blood material for the purpose of function, for cell repair and
renewal, and the products of waste must be removed. In the injury
which has been produced in the tissue all the cells have suffered,
some possibly displaced from their connections, others may have been
completely destroyed, others have sustained varying degrees of injury.
If the injury be of an infectious character, that is, produced by
bacteria, these may be present in the part and continue to exert
injury by the poisonous substances which they produce, or if the
injury has been produced by the action of some other sort of poison,
this may be present in concentrated form, or the injury may have been
the result of the presence of a foreign body in the part. Under these
conditions, since the usual activities of the cells in the injured
part will not suffice to restore the integrity of the tissue, repair
and cell formation must be more active than usual, any injurious
substances must be removed or such changes must take place in the
tissue that the cell life adapts itself to new conditions.
[Illustration: FIG. 16.--PHAGOCYTOSIS. _a_, _b_, _c_ are the
microphages or the bacterial phagocytes. (_a_) Contains a number of
round bacteria, and (_b_) similar bacteria arranged in chains, and
(_c_) a number of rod-shaped bacteria (_d_) Is a cell phagocyte or
macrophage which contains five red blood corpuscles.]
All life in the tissues depends upon the circulation of the blood.
There is definite relation between the activity of cells and the blood
supply; a part, for instance, which is in active function receives a
greater supply of blood by means of dilatation of the arteries which
supply it. If the body be exactly balanced longitudinally on a
platform, reading or any exercise of the brain causes the head end to
sink owing to the relatively greater amount of blood which the brain
receives when in active function. The regulation of the blood supply
is effected by means of nerves which act upon the muscular walls of
the arteries causing, by the contraction or the relaxation of the
muscle, diminution or dilatation of the calibre of the vessel. After
injury the dilatation of the vessels with the greater afflux of blood
to the part is the effect of the greatly increased cell activity, and
is a necessity for this. In many forms of disease it has been found
that by increasing the blood flow to a part and producing an active
circulation in it, that recovery more readily takes place and many of
the procedures which have been found useful in inflammation, such as
hot applications, act by increasing the blood flow. So intimate is the
association between cell activity, as shown in repair and new
formation of cells, and the blood flow, that new blood vessels
frequently develop by means of which the capacity for nutrition is
still more increased. The cornea or transparent part of the eye
contains no blood vessels, the cells which it contains being nourished
by the tissue fluid which comes from the outside and circulates in
small communicating spaces. If the centre of the cornea be injured,
the cells of the blood vessels in the tissue around the cornea
multiply and form new vessels which grow into the cornea and appear as
a pink fringe around the periphery; when repair has taken place the
newly formed vessels disappear.
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