The heat of the inflamed part is to be attributed to the increased quantity of blood present in it, and the more superficial the affected area the more readily is the local increase of temperature detected by the hand.  This clinical point is best tested by placing the palm of the hand and fingers for a few seconds alternately over an uninflamed and an inflamed area, otherwise under similar conditions as to coverings and exposure.  In this way even slight differences may be recognised.

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, hyperaemic 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 oedema.  The more open the structure of the tissue of the part, the greater is the amount of swelling—­witness the marked degree of oedema 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 periosteum or bone, or in encapsuled organs, as dull, boring, or aching.  When inflammation is passing on to suppuration the pain assumes a throbbing character, and as the pus reaches the surface, or “points,” as it is called, sharp, darting, or lancinating pains are experienced.  Inflammation involving a nerve-trunk may cause a boring or a tingling pain; while the implication of a serous membrane such as the pleura or peritoneum gives rise to a pain of a sharp, stabbing character.

Interference with the function of the inflamed part is always present to a greater or less extent.