_Redness_, similarly, is due to the increased afflux of blood to the
inflamed part. The shade of colour varies with the stage of the
inflammation, being lighter and brighter in the early, hyperæmic stages,
and darker and duskier when the blood flow is slowed or when stasis has
occurred and the oxygenation of the blood is defective. In the
thrombotic stage the part may assume a purplish hue.

The _swelling_ is partly due to the increased amount of blood in the
affected part and to the accumulation of leucocytes and proliferated
tissue cells, but chiefly to the exudate in the connective
tissue--_inflammatory œdema_. The more open the structure of the tissue
of the part, the greater is the amount of swelling--witness the marked
degree of œdema that occurs in such parts as the scrotum or the eyelids.

_Pain_ is a symptom seldom absent in inflammation. _Tenderness_--that
is, pain elicited on pressure--is one of the most valuable diagnostic
signs we possess, and is often present before pain is experienced by the
patient. That the area of tenderness corresponds to the area of
inflammation is almost an axiom of surgery. Pain and tenderness are due
to the irritation of nerve filaments of the part, rendered all the more
sensitive by the abnormal conditions of their blood supply. In
inflammatory conditions of internal organs, for example the abdominal
viscera, the pain is frequently referred to other parts, usually to an
area supplied by branches from the same segment of the cord as that
supplying the inflamed part.

For purposes of diagnosis, attention should be paid to the terms in
which the patient describes his pain. For example, the pain caused by
an inflammation of the skin is usually described as of a _burning_ or
_itching_ character; that of inflammation in dense tissues like