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.

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.