This general increase of the secretions renders emetics useful in various conditions of disease; whenever, indeed, there may be deficiency of action in any one of the surfaces or glands upon which they more especially operate, and of course in febrile diseases, in which there is often a general deficiency of secretions. it does not follow, however, that emetics are to be used in all these cases. Not unfrequently contraindications exist; and, when this may not be the case, there are generally other and less disagreeable methods of bringing about the same result. Nevertheless, the practitioner should be familiar with this therapeutic effect of emetics, so that he may have recourse to it, should the occasion offer.

One affection in which emetics often operate very happily, upon this principle, is jaundice. I have elsewhere endeavoured to demonstrate that, in the great majority of cases, this disease is the immediate result of diminution in the secretory function of the liver. Sometimes the disease is obstinate, and resists the ordinary hepatic stimulants. in such instances, emetics occasionally operate most happily; bringing, as they do, so many different agencies to bear upon that organ, all calculated to promote its secretory function.

6. Depletion. Emetics deplete in two ways; first, directly by increasing secretion, and secondly, indirectly, by removing from the stomach, and sometimes from the duodenum, materials which would otherwise make their way into the circulation, and increase or enrich the blood. Upon this principle, they are useful in plethora, vascular irritation or active congestion, and inflammation. But they are seldom used purposely with reference to this special effect; as the same ends can be accomplished by less disagreeable, and probably more effective means. Still they may act incidentally with advantage upon this principle, when given for other purposes; and their depletory effect should be taken into consideration, in estimating the indications for their use. it may turn the scale in their favour, when equally balanced by other considerations.

1. Promotion of Absorption. This property of emetics follows as a necessary consequence of their depletory powers. Whatever removes blood, or any constituent of the blood, from the circulation, favours absorption into it; and this is especially true of the liquid ingredients. The relaxed and flaccid condition of the blood-vessels has also, probably, the tendency to produce a contrary and balancing condition of the absorbents. By this property of promoting absorption, emetics occasionally prove beneficial in dropsies; though seldom used purposely for this end. They have sometimes been employed, and with considerable efficiency too, upon this principle, to aid in the resolution of obstinate swellings of the testicles, and of the absorbent glands.

8. Revulsion. This principle in the operation of medicines has already been explained. (See vol. i. p. 49.) By their irritant action on the stomach, whether directly or through the circulation, emetics attract the arterial blood and the nervous energy to the gastric and duodenal mucous membrane, and thereby draw them from other parts where they may have been unduly concentrated. Upon this principle, in co-operation with others already referred to, they act beneficially in vascular irritation and inflammation, seated in remote parts. Hence, in part, their usefulness in inflammations and spasmodic affections of the air-passages, the fauces including the tonsils, and the lungs, when employed in the early stages. Hence too their powerful influence over cerebral excitement, especially when so managed as to sustain a nauseating effect, instead of being pushed to positive emesis. in congestion of the brain, of an apoplectic character, they are somewhat hazardous; but, when the excitement is mainly nervous, they often act very powerfully and advantageously. Few remedies are more efficient in maniacal or delirious violence, and cerebral excitement of a hysterical character, than emetics, so given as to nauseate. in amaurosis, dependent on irritation of the nervous centre of vision, they sometimes act happily. They have been recommended also in delirium tremens. in cases of gout and rheumatism, they operate usefully on the same principle.

In hemorrhages, too, they have been employed upon the same indication; and occasionally with considerable success, especially in that of the uterus.

In neuralgic affections they often operate beneficially, probably in part at least, upon this principle of revulsion. They may be tried in any obstinate case, but are more particularly adapted to the disease when it affects the head. The late Dr. Physick used to recommend them, as the most efficient means of cure, in those obstinate pains in the scalp, occupying the seat of a former bruise or other injury.

But, with a view to revulsion, they cannot of course be used in inflammation or hemorrhage of the stomach itself, or the organs in its immediate vicinity; though it is not impossible that, in other ways, they may prove beneficial in these affections.

9. A Shock on the System. The influence of emetics is rapid, powerful, and extensive. it is felt by the abdominal viscera, the brain, the heart, and, in fact, by every sensitive part of the body. They produce, therefore, a sort of shock upon the system, well calculated to rouse it out of torpor, and to unseat diseases which may have fixed themselves but recently, and with no great tenacity of hold, in the tissues. in this way they may break the chain of morbid associations, upon which the continuance of disease probably often depends. They substitute their own temporary influence immediately, or by anticipation, for that of other morbid agency, and thus operate on the principle of supersession. (See vol. i. p. 51.) it is in this way, probably, that they prove efficacious in preventing the paroxysms of periodical diseases, being administered so as to be in full operation about the time of the expected attack. They will thus often prevent the paroxysms of intermittent and remittent fevers, and of intermittent neuralgia; and, upon the same principle, if given at the original approach of one of the miasmatic fevers, may altogether set it aside.