Functional derangements of a primary character may be enumerated as irritation, inflammation, congestion, depression, and fever.

Irritation

Irritation is a condition in which there is an abnormally increased activity in a part, due to morbid excitation caused by some abnormal influence, mechanical, chemical, or physical.

Congestion

Congestion is a condition of a part or organ in which the small blood-vessels contain an unnatural quantity of blood. There are two forms, active and passive. In active congestion there is abnormal activity of the circulation, which is the result of irritation or unnatural excitement of the vital activities of a part. In passive congestion there is no increase in the amount of blood circulating through the part. In fact, the amount of blood actually passing through its blood vessels may be diminished. The condition is one in which from some obstruction to the circulation the venous blood does not pass onward as rapidly as it should, and hence accumulates. The accumulation may be the result of mechanical obstruction of the circulation or deficiency in the vital activity of the tissues. Passive congestion is always accompanied with a depressed condition of the affected part. The results of congestion depend on the nature of the organ affected. Whether active or passive, it always causes a decided disturbance of the functions of the part. If a secreting or excreting organ is affected, the natural product may be increased or diminished according to the intensity and character of the congestion. Congestion, both active and passive, is often accompanied with pain. The pain of active congestion is much more acute than that of passive congestion. Active congestion is of short duration, as if long continued it passes into inflammation or passive congestion.

Inflammation

Inflammation is a morbid condition, the symptoms of which are usually described as being heat, pain, redness, and swelling. It should be mentioned, however, that the symptoms given are not the real disease. Inflammation itself is undoubtedly only an advanced stage of the condition before described as irritation. When irritation becomes intense or is sufficiently long continued, certain changes in the tissues occur which are recognized as inflammation. One of the first and mast characteristic symptoms is an increase in the number of white blood corpuscles in the part subject to the morbid process. The heat, pain, redness, and swelling are for the most part due to the increased blood supply, although no doubt a portion of the increased amount of heat is caused by the abnormal activity of the tissues of the diseased part. The results of inflammation, like those of depression, depend in some degree upon the part affected. As we shall mention in particular the inflammation of various parts of the body, we need not dwell further upon the subject here.

Depression

Depression, either local or general, is a condition in which there is deficient vital activity. It may be the result of a deficient supply, of the natural agents upon which the system depends for support, as heat, light, electricity, food, and pure air, or it may be the result of too intense and prolonged activity, or the influence of some noxious agent upon the system, as powerful poisons. It is always present in anemia and all forms of debility. It is probable also that various degenerations previously described, and probably also morbid growths, as well as tubercles, are due to depression, since it is observed that these morbid conditions almost universally occur in connection with conditions of general or local debility.

Fever

Fever is a morbid process somewhat difficult to describe. It is. perhaps hardly primary in character, since it may include all the other functional derangements mentioned. Fever is always characterized by an elevation of temperature, a change in the frequency and force of the pulse, and a disturbance in greater or lesser degree of the functions; of every organ of the body. The various minor symptoms of fever-wili be noticed elsewhere, and the peculiar characteristics of the various individual fevers will be given in connection with their description.