The arteries and veins dilate and the circulation is quickened. After a brief time the rate of circulation in the dilated vessels slows down until it is slower than normal. The web becomes swollen from the increased amount of fluid and blood corpuscles that are forced out of the blood vessels into the tissues in and around the injured section. The injured point becomes very sensitive, even painful and hot. This gives us the four cardinal symptoms of inflammation--redness, heat, pain, and swelling; to which a fifth has been added--more or less complete loss of function. All of these symptoms are due to the unusual amount of blood and blood plasma in the tissues. The increased temperature is due to the increased amount of blood in the parts, the redness is due to the same cause, as is the swelling and pain--the pain being due chiefly to the increased pressure upon the sensory nerves.

These "signs of inflammation"--heat, redness, pain, increase of size of the part and modified function--are more or less constant. Organs not supplied with sensory nerves, or but slightly supplied with sensory nerves, as the heart, liver, spleen, kidneys, lungs, stomach, etc., may be inflamed without any pain accompanying the inflammation. There will be swelling, redness, heat, and impaired function, but little or no pain. There is even little redness in inflammation of such tissues as cartilages, ligaments, osseous tissues, muscular fascia, serous membranes, etc.

Briefly defined, inflammation is a local and circumscribed accumulation of blood, with increase of fundamental vital action and decrease of special function in the part.

The increased blood sent to the injured part serves as food to be used in repairing damages and serves also protective purposes in meeting, diluting and decomposing drugs or infectious matters.

The life of cells in a complex body depends upon the circulation of its blood and lymph. There exists a definite relationship between the blood supply of a part and the activity of its cells. The action of muscles calls for a greater supply of blood to these. The digestion of a meal calls for an increased amount of blood to the organs of digestion. Thinking demands more blood to the brain. The ripening of an ovum demands that more blood be sent to the ovaries. The repair of an injury calls for extra blood at the point of injury.

"Ubi irritatio ibi affluxus"--where irritation is, there the blood flows--was long a medical maxim. Since the amount of blood in a part determines its health and action and its ability to meet and overcome injuries, irritants and toxins, etc., nothing could be more natural, or more fully in harmony with the laws of life, than the establishment of inflammation as a means of protection against outside encroachments and to repair damaged structures. By inflammation wounds are closed, broken bones repaired and foreign and injurious bodies and substances are carried out of the body. The increased blood in the part supplies it with a greater amount of nutritive material and thus hastens healing. Microscopic examination of an inflamed section shows all the cells in that area, even those forming the walls of the blood vessels, to be swollen, while their nuclei contain chromatin. There are changes in the nuclei which indicate that the cells are multiplying. Their is every indication of a more active life within that section.

So greatly does the increased cellular activity necessary for repair depend upon an increased blood supply that new blood vessels frequently develop. In this way the capacity for nutrition is greatly increased. An excellent example of this is seen in the eye. The cornea of the eye contains no blood vessels. Its cells are nourished from the lymph which comes to it from the tissues at its outside. If the center of the cornea is injured, the cells of the blood vessels surrounding the cornea multiply and form new vessels. These appear as a pink fringe around the corneal periphery. When the process of repair is completed the new blood vessels disappear.

Under abnormal conditions, the usual activities of the injured cells are not sufficient to restore the integrity of the injured tissue. It is essential that the processes of cell-formation and repair be accelerated and all injurious substances removed, or else such changes must take place in the cells as will adapt them to new conditions of life. The blood vessels dilate and new vessels are formed thus carrying more nutritive material to the part. This excess nutritive material exudes into the tissues surrounding the point of injury as well as into the injured section. This serves several purposes.

It dilutes any injurious substance that may have found its way into the tissue. Drop a crystal of salt into your eye. It is highly irritating. Dilute such a crystal in a small amount of water and the solution produces little or no irritation. Drugs, bacterial execretions, etc., are diluted and carried away from the point of injury; or, the character of such poisons may be so changed as to render them less harmful or not harmful at all.

Inflammation is a great accumulation of blood in an organ or tissue in response to an irritant, or injury, to repair the damages and remove or counteract the irritant. It is not "disease" at all but a simple effort of the organism to remove the cause of "disease" or to repair the damages. It is a remedy and as such is protective and constructive. It has been said that "inflammation is a local fever and that fever is a general inflammation." If this means that they are both parts of the same healing process we do not object, but a general inflammation could not exist because of lack of sufficient blood in the body to produce it.

Inflammation is a vital act and, while it may be obstructed and rendered inefficient and a failure, its character is never changed from physiological to pathological. It is the vital process of healing in every instance of damaged tissue. It is the natural and necessary result of the concentration of the healing forces and materials at any given part to heal or preserve it.

Just as all physiological acts demand and receive an extra supply of blood (an extra supply of blood is demanded by active muscles; by secreting glands; by the stomach that is digesting food; by an active brain), so an increase of blood is demanded by an injured or irritated part to repair the injury and resist and overcome the irritant.

Not only is the nutritive material sent to the part in greater abundance than under normal conditions, but its character differs somewhat. Ordinarily, those substances upon which coagulation of the blood depends pass out through the walls of the blood vessels to a very slight extent. But in cases of injury the coagulable substance may be present in such amounts that the exudate easily clots. Calcification, granulation, fibrin formation, etc., result. These are all defense measures.