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ELEMENTS OF MATERIA MEDICA.

The intensity and duration of the different stages of vomiting have nonecessary relation to each other. Thus the sulphates of zinc and copperexcite speedy vomiting, with but little nausea;—and are, therefore,preferred as emetics in narcotic poisoning. Tobacco and tartarizedantimony, on the other hand, produce great nausea and depression ofsystem.

The causes of vomiting are various. One is, suddenly distending thestomach with warm water or demulcent liquids. In cases of corrosive orirritant poisoning, we adopt this method of exciting or promoting vomit-ing in preference to the use of acrid substances. Another method ofprovoking vomiting is tickling the fauces with the finger or a feather:this has been shewn by Dr. M. Hall to be a beautiful instance of reflexaction. We adopt this plan in cases of poisoning until the ordinaryemetics can be procured,—also in dyspepsia and cardialgia, arisingfrom the presence of undigested food in the stomach. Acrids and irri-tants of all kinds likewise excite vomiting when swallowed. Thusgamboge, mustard, common salt, euphorbium, the mineral acids, &c.,have this effect when taken in large or poisonous doses. Most of these,however, are dangerous agents, and, with the exception of mustard andcommon salt, are not given as emetics. The last-mentioned substancesare administered to excite vomiting in cases of narcotic poisoning, inmalignant cholera, &c. But there are certain irritants (such as tartar-emetic and ipecacuanha) which seem to have some specific power ofprovoking vomiting, since they produce this effect when applied to anypart of the body, or when injected into the veins. These are the agentsto which the term emetic is more usually applied.

Besides the above, there are many other causes of vomiting, such asacute pain, injuries of the brain, calculi in the kidneys, disagreeableodours, the sight of disgusting objects, whirling, sailing, or swing-ing, &c.

The irritation produced by the exhibition of emetics gives rise to anincreased secretion from the mucous follicles of the stomach and duode-num ; as is apparently shewn by the thick, filamentous, and viscidmatters frequently ejected. We infer, also, that the action of the exhal-ing vessels must be increased, inasmuch as persons who have taken onlya few spoonfuls of emetic liquids sometimes bring up a very conside-rable quantity of water. Darwin mentions a man who vomited sixpints of liquid, although he had only swallowed one. Bile is fre-quently thrown up, either alone or mixed with other fluids; but we mustnot infer from this that it had existed in the stomach previous to theexhibition of the emetic, for bile is not ordinarily rejected in the firstefforts, but only in the subsequent vomitings; and the quantity increasesin proportion to the length of time the vomiting continues. It is gene-rally supposed that emetics promote the secretion of bile and of pan-creatic juice.

6. Carthartics or Purgatives .—These are medicinal agents which ex-cite alvine evacuations. They do so by increasing the peristaltic motionof the alimentary canal, and by promoting secretion and exhalation fromthe mucous lining. It has been supposed that some of them stimulatethe muscular coat of the intestine, without increasing the secretions,—and, vice versa, that others stimulate the mucous follicles and exhaling