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Vomiting, when produced by the operation of a mild emetic, does not appear to exhaust the excitability of the stomach, but on the contrary to increase its tone; for we generally find the process of digestion is carried on more vigorously afterwards; although it is probable that, by frequent repetition, a different result would be obtained, and we should find that its motion would become liable to inversion by slight stimuli: we may therefore question the propriety of that practice which is so strenuously recommended by Hippocrates,^[152] and other ancient physicians, to administer emetics frequently to those in health, in order to prevent the incursions of disease.

The benefits arising from the secondary effects of an emetic are numerous and extensive. It has been observed that during nausea the force of the circulation is considerably abated, hence the use of these remedies in hemorrhage; and, as the energy of absorption is generally in an inverse ratio to that of the circulation,^[153] we frequently obtain from a nauseating dose of an emetic, considerable assistance in the treatment of anasarca, and other dropsical swellings. Those medicines that are liable to produce at once, full vomiting, without any previous stage of nausea, are of course less calculated to fulfil such indications. In the same manner we should select a nauseating emetic, when our object is to promote the passage of a gall stone through the ductus communis, for the nausea so excited will relax the duct, while the mechanical concussion tends to push the obstructing matter forward. On the other hand, whenever our object is to evacuate the stomach, and to prevent absorption, we must take care to cut short the nauseating stage; a precaution which is highly important in the treatment of a case of poisoning. The state of the stomach produced by vomiting is very frequently extended, by sympathy, to the vessels of the skin; in consequence of which, a diaphoresis not unusually follows the operation. In the different varieties of febrile disease, this circumstance stamps additional value upon the class of Emetics; while, at the same time, that they eject any offensive matter which may be present in the stomach, they thus control the accelerated circulation.