Vomiting, the act of rejecting the contents of the stomach, due in great part to the contraction of the abdominal muscles, assisted by the active cooperation of the muscular walls of the organ; the diaphragm remains fixed, affording a firm surface against which the stomach is pressed by the abdominal muscles. Relaxation of the sphincter at the cardiac orifice of the stomach is necessary, as its contraction will resist the power of all the expulsor muscles combined, explaining the violent and vain efforts to vomit which all must have seen or experienced; the act is preceded by a deep inspiration, the glottis being spasmodically closed during the paroxysm. It may be produced by irritating substances applied to the mucous membrane of the stomach, the impression being conveyed by the pneumogastric nerves and the motor nerves of expiration, as with common emetics; by irritations in other parts of the body, transmitted by reflex nervous action, as in strangulated hernia, the passage of calculi, and during gestation; and by impressions received through the sensorial centres, whether emotional or sensational, as from tickling the fauces, disgusting sights or odors, and in sea sickness; even the recollection of these sensations may cause vomiting in very impressionable persons.

It is a common symptom of many diseases of the stomach and intestines, and arises from sympathy in affections of many other organs; it is sometimes nervous or spasmodic. Vomiting usually acts as its own remedy, the expulsion of the irritating contents of the stomach, when complete, being as a general rule sufficient to relieve the system from any further disturbance. When due to other causes, as for example sea sickness, early pregnancy, etc, it is also for the most part temporary, and subsides spontaneously after a certain period. When long continued and obstinate, or unusually violent, it may require the use of special remedies, such as bits of ice held in the mouth and slowly swallowed, small doses of chloroform or hydrocyanic acid, or the application of sinapisms or blisters to the epigastrium.