The system sympathises much more with some parts than with others; and we accordingly find that disorder in one part will give rise to alarming constitutional excitement, whilst in another, a much greater derangement in function and structure will apparently be almost entirely disregarded by the constitution. _Irritation_ is an effect of sympathy, and differs from inflammation, inasmuch as the functions of the nervous system, and not those of the sanguiferous, are disturbed;—the latter frequently supervenes on the former. Irritation is local, or constitutional. As examples of the strictly local species, may be mentioned that peculiar and dreadfully annoying sensation produced in the alveoli by the presence of a diseased tooth, or the irritation caused by ascarides in the rectum, or by stone in the bladder. But, from this action being dependent on the nervous agency, irritation is frequently produced in a part remote from the source of the action. Thus, if an irritating cause of any kind be applied to the origin of a nerve, the effects of the irritation may be evinced in a part supplied by its extreme branches; while, if the cause is applied to the termination of a nerve, a similar action is produced at its commencement, and in parts supplied by nerves from the same origin. Thus, disease of the hip-joint causes pain in the knee, whilst dentition in children not unfrequently produces fatal effusion at the base of the brain; and again, irritation at the neck of the bladder frequently gives rise to pain in the feet. Local impressions, injuries, or irritations, though apparently of little importance, frequently produce irritation which affects the whole system, and is therefore termed _constitutional_. Syncope sometimes follows the passing of a bougie along the urethra. We meet with too many instances of constitutional irritation following severe injuries or operations, especially if attended with much hemorrhage. In general, there is considerable prostration of strength; the patient is anxious and restless; his sleep is disturbed; the pulse is weak and fluttering, occasionally intermittent; the tongue is white and loaded; the appetite is gone; the stomach rejects the little food which the patient is able to take; he is startled and annoyed by the slightest external impression. At this period of the disorder, rigors generally occur, and are followed by a sense of heat, and by perspiration; then the above symptoms gradually decrease, and the patient recovers; but in certain instances his breathing becomes quick and somewhat oppressed, attended with a peculiar spasmodic elevation of the nostrils; all the secretions are diminished, the intellectual functions become impaired, and there are occasional convulsive twitchings; coma supervenes, preceded by a low muttering delirium, and followed by death.