Emetics, (from to vomit,) anocathartica, and -uomitoria; medicines which excite vomiting.
The use of these medicines is so extensive, and their effects often so important, that they will justify our considering them at some length. The most simple view we can take of emetics is, that they evacuate the stomach by the inverted action of its own motions with those of the oesophagus, assisted by the contraction of the diaphragm and abdominal muscles. This alone is an object of no little importance when we consider the extensive influence of this organ, and the very dangerous consequences which arise from its acrimonious or vitiated contents. But the advantages do not rest here. The same inverted motion is communicated to the duodenum, and, in some degree, to the inferior partsof the canal. Into this second stomach, as we have described it, the bile and pancreatic juice are poured; and, while the joint action of the diaphragm and the abdominal muscles compress the gall bladder to evacuate its contents, the inverted motion of the duodenum and stomach evacuate it. Emetics, in this way, unite with cathartics in assisting the secretion and discharge of bile; in relieving or preventing infarctions of the liver: for, while the latter promote the secretion by stimulating the ducts, the former contribute to the same purpose by an action more strictly mechanical.
We have often had occasion to remark the extensive influence of the stomach in the animal economy, particularly its connexion with the state of the brain and the extreme vessels. The first effect of emetics, in consequence of this connexion, is to produce a general relaxation, approaching sometimes to faintness. In this state the extreme vessels sympathise and yield, with little resistance, to the force of the circulation. Perspiration follows, which by the action of vomiting is still further increased; and, if this is kept up by other means, the most salutary changes are often produced. "We perceive the connexion of the stomach with the head, rather in the morbid than the salutary effects. During the action of vomiting, the return of the blood from the head is impeded, and all its vessels are distended; which has occasioned some hesitation in the use of emetics, when these vessels were previously distended, as in apoplexy and palsy. In such circumstances, however, we find the irritation on the brain communicated to the stomach, and vomiting excited.
The agitation of vomiting has been considered as useful; but this is a vague, indistinct indication. Medicines of this kind have, however, been employed where obstructions have been suspected; and, in the brain, the alternate filling and emptying their vessels may contribute to excite and support their action. We see some traces of such an influence from their utility in nervous diseases, particularly in those attended with general languor, as hypochondriasis, and in obstructed menses; but more strikingly in the good effects of very active emetics, particularly of vitriolated mercury in the cure of gutta serena. Another distant effect of emetics is more certain: their increasing the action of the absorbent system. Their operation, in this way, is not easily explained, but such effects are well established; and, on this account, we shall find them extremely ser-viceable, when we wish to promote the absorption of purulent matter that we cannot with ease or safety evacuate. They cannot be employed to relieve the more extensive accumulations of dropsies.
A very important effect of emetics, referrible in part to their action, and sometimes, perhaps, to the nature of the medicine, is their power of emulging the bronchial glands. On the first access of nausea, we find a flow of saliva, and a little discharge from the bronchiae; but, when the emetic begins to act with some violence, this discharge is considerable; and no remedy is more powerful in producing a complete evacuation of those glands, or relieving them from the infarctions of viscid mucus. In part, this effect may be owing to the medicine; for we shall find some of the most active emetics to be expectorants also.
Emetics are of very different kinds. Some are purely stimulant, as mustard, volatile alkali, and horse radish root. Others are sedative or relaxant. Opium, in large doses, acts as an emetic. Foxglove, tobacco, putrid substances, oil, and warm water, are emetics of different strength, nearly in their order. The greater number, however, act apparently by a peculiar stimulus. In some of these the stimulus is obvious; and, when the stomach is not affected, acts on other secretory organs. The principal emetics of this kind are the antimonial preparations, which affect the bowels, the skin, and sometimes the bronchial glands. The mercurials are similar in this respect; but the copper, zinc, and platina, which in all their forms are emetic, seem not to affect any other glands. The acrimony of the squill and the seneka root is very general: they are not only emetics, but cathartics and expectorants. The asarabacca and the groundsel juice are more limited in their stimulant powers. The former, besides its emetic property, acts chiefly as an errhine, and the latter only on the intestines. The ipecacuanha is the connecting link between these more general stimulants and medicines, which seem to act from a specific influence on the stomach. There are certainly emetics which may be referred to this head. The vitriols of zinc, already mentioned, not to separate the metallic substances, have little general stimulus; and the air of the lungs which, when swallowed, proves certainly emetic, is wholly without any other power. Every nauseous taste tends to excite the action of the stomach; and to this head may be referred the bitters, as wormwood, camomile flowers, the seeds of the carduus benedictus and broom. Putrid substances, and the liver of sulphur, act apparently in the same way.