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Page 20
CHAPTER IV
THE REACTIONS OF THE TISSUES OF THE BODY TO INJURIES.--INFLAMMATION.--
THE CHANGES IN THE BLOOD IN THIS.--THE EMIGRATION OF THE CORPUSCLES OF
THE BLOOD.--THE EVIDENT CHANGES IN THE INJURED PART AND THE MANNER IN
WHICH THESE ARE PRODUCED.--HEAT, REDNESS, SWELLING AND PAIN.--THE
PRODUCTION OF BLISTERS BY SUNBURN.--THE CHANGES IN THE CELLS OF AN
INJURED PART.--THE CELLS WHICH MIGRATE FROM THE BLOOD-VESSELS ACT AS
PHAGOCYTES.--THE MACROPHAGES.--THE MICROPHAGES.--CHEMOTROPISM.--THE
HEALING OF INFLAMMATION.--THE REMOVAL OF THE CAUSE.--CELL REPAIR AND
NEW FORMATION.--NEW FORMATION OF BLOOD-VESSELS.--ACUTE AND CHRONIC
INFLAMMATION.--THE APPARENTLY PURPOSEFUL CHARACTER OF THE CHANGES IN
INFLAMMATION.
Injury and repair have already been briefly considered in their
relation to the normal body and to old age; there are, however,
certain phenomena included under the term inflammation which follow
the more extensive injuries and demand a closer consideration than was
given in Chapter II. These phenomena differ in degree and character;
they are affected by the nature of the injurious agent and the
intensity of its action, by the character of the tissue which is
affected and by variations in individual resistance to injury. A blow
which would have no effect upon the general surface of the body may
produce serious results if it fall upon the eye, and less serious
results for a robust than for a weak individual.
Most of the changes which take place after an injury and their
sequence can be followed under the microscope. If the thin membrane
between the toes of a living frog be placed under the microscope the
blood vessels and the circulating blood can be distinctly seen in the
thin tissue between the transparent surfaces. The arteries, the
capillaries and veins can be distinguished, the arteries by the
changing rapidity of the blood stream within them, there being a
quickening of the flow corresponding with each contraction of the
heart; the veins appear as large vessels in which the blood flows
regularly (Fig. 11). Between the veins and arteries is a large number
of capillaries with thin transparent walls and a diameter no greater
than that of the single blood corpuscles; they receive the blood from
the arteries and the flow in them is continuous. The white and red
blood corpuscles can be distinguished, the red appearing as oval discs
and the white as colorless spheres. In the arteries and veins the red
corpuscles remain in the centre of the vessels appearing as a rapidly
moving red core, and between this core and the wall of the vessels is
a layer of clear fluid in which the white corpuscles move more slowly,
often turning over and over as a ball rolls along the table.
If, now, the web be injured by pricking it or placing some irritating
substance upon it, a change takes place in the circulation. The
arteries and the veins become dilated and the flow of blood more
rapid, so rapid, indeed, that it is difficult to distinguish the
single corpuscles. In a short while the rapidity of flow in the
dilated vessels diminishes, becoming slower than the normal, and the
separation between the red and white corpuscles is not so evident. In
the slowly moving stream the white corpuscles move much more slowly
than do the red, and hence accumulate in the vessels lining the inner
surface and later become attached to this and cease to move forward.
The attached corpuscles then begin to move as does an amoeba, sending
out projections, some one of which penetrates the wall, and following
this the corpuscles creep through. Red corpuscles also pass out of the
vessels, this taking place in the capillaries; the white corpuscles,
on the other hand, pass through the small veins. Not only do the white
corpuscles pass through the vessels, but the blood fluid also passes
out. The corpuscles which have passed into the tissue around the
vessels are carried away by the outstreaming fluid, and the web
becomes swollen from the increased amount of fluid which it contains.
The injured area of the web is more sensitive than a corresponding
uninjured area and the foot is more quickly moved if it be touched. If
the injury has been very slight, observation of the area on the
following day will show no change beyond a slight dilatation of the
vessels and a great accumulation of cells in the tissue.
Everyone has experienced the effect of such changes as have been
described in this simple experiment. An inflamed part on the surface
of the body is redder than the normal, swollen, hot and painful. The
usual red tinge of the skin is due to the red blood contained in the
vessels, and the color is intensified when, owing to the dilatation,
the vessels contain more blood. The inflamed area feels hot, and if
the temperature be taken it may be two or three degrees warmer than a
corresponding area. The increased heat is due to the richer
circulation. Heat is produced in the interior of the body chiefly in
the muscles and great glands, and the increased afflux of blood brings
more heat to the surface. A certain degree of swelling of the tissue
is due to the dilatation of the vessels; but this is a negligible
factor as compared with the effect of the presence of the fluid and
cells of the exudate.[1] The fluid distends the tissue spaces, and it
may pass from the tissue and accumulate on surfaces or in the large
cavities within the body. The greatly increased discharge from the
nose in a "cold in the head" is due to the exudation formed in the
acutely inflamed tissue, and which readily passes through the thin
epithelial covering. Various degrees of inflammation of the skin may
be produced by the action of the sun, the injury being due not to the
heat but to the actinic rays. In a mild degree of exposure only
redness and a strong sense of heat are produced, but in prolonged
exposure an exudate is formed which causes the skin to swell and
blisters to form, these being due to the exudate which passes through
the lower layers of the cells of the epidermis and collects beneath
the impervious upper layer, detaching this from its connections. If a
small wad of cotton, soaked in strong ammonia, be placed on the skin
and covered with a thimble and removed after two minutes, minute
blisters of exudate slowly form at the spot.
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