All emetic substances, which have the nauseating property in any considerable degree, are capable of operating as diaphoretics. in the condition of nausea, as explained in the preceding general observations, there is a universal relaxation of the cutaneous capillaries, by which the watery parts of the blood are permitted to ooze through their coats, constituting perspiration. Whether this transudation is a mere mechanical process, or regulated in some measure by the vital force, is a question which it would not be easy to solve; but this fact is evident, that it is not the unaltered liquor sanguinis that exudes, for the liquid neither coagulates spontaneously like fibrin, nor with the aid of heat like albumen. it, therefore, undergoes some modification in its passage, which is probably owing to the influence of the membranous tissue through which it oozes; but whether this influence is physical or vital has not been determined. Whatever may be the fact in this respect, the exudation appears to be quite distinct from the process by which the follicular cells elaborate the proper perspiratory secretion.

But these medicines will often produce a diaphoretic effect in doses insufficient to cause any sensible nausea. It is probable, nevertheless, that they still exercise on the nervous centres a degree of the same influence, which, though not strong enough to give rise to the positive sensation of nausea, may occasion, in a slighter degree, the relaxation of surface characteristic of the nauseating influence.

There is, however, an additional method in which some, if not all of the nauseating diaphoretics operate. The perspiratory effect first mentioned results from a sympathetic impression made on the surface through the nervous centres. That now referred to. proceeds from their absorption, and direct excitant influence on the proper secretory structure of the skin. I have no doubt that tartar emetic at least operates in this double way.

Though all the nauseating medicines are diaphoretic, there are only two which are much used in this country, namely, tartar emetic, and ipecacuanha. The other preparations of antimony are sometimes employed, especially in Europe; and American practitioners occasionally resort to our indigenous emetics, as sanguinaria and lobelia; but all the advantages that are afforded by these substances as diaphoretics can be equally obtained from the two first mentioned, to which I shall confine my observations. For all that is necessary to be known in relation to the other antimonials, the reader is referred to the article on the preparations of antimony, under the arterial sedatives (ii. 76); and lobelia and sanguinaria will be found described among the emetics.