Tartar emetic may produce all the foregoing effects without giving rise to nausea; but, from a certain amount of it, which differs extremely under different circumstances, this effect almost always ensues, attended or soon followed by vomiting, which is often violent and repeated. it is, indeed, one of our most efficient emetics, and is among those which are most nauseating. The sensation of nausea, from this as from other causes, is accompanied with certain highly characteristic phenomena, all of which are of a sedative character, and, when they occur, add greatly to the prostration occasioned by the direct sedative action of the medicine. With distressing sensations of sinking or other uneasiness in the epigastrium, there are feelings of great languor and mental depression, muscular relaxation and weakness, shrunken and anxious features, feebleness and irregularity of the pulse, paleness and coolness of the surface, and often copious sweating. it is when tartar emetic nauseates that it is most apt to operate as a diaphoretic, and operates most freely; but it is by no means true that it never produces the latter effect, unless through the instrumentality of the former.

Of the influence of tartar emetic over the secretions, as well as of its nauseating and emetic properties, I shall have occasion to treat more fully hereafter. it is as an arterial sedative that we are here specially to consider it.

Within a comparatively short period of time, attention has been called to the extraordinary powers which this medicine evinces, when very largely administered, of reducing the circulation, respiration, and temperature, without, under certain circumstances, acting as an emetic, or in any considerable degree even nauseating. it was formerly supposed that, in large doses, tartar emetic must almost certainly nauseate and vomit, and that these effects, instead of diminishing or disappearing upon frequent repetition of the dose, were usually increased. The contrary of this has been ascertained to occur very frequently. Two or three grains of the medicine will generally be sufficient to vomit, and from six to twelve grains almost always; yet Rasori is stated to have given several drachms daily, and several ounces in the course of a single attack of disease, without the occurrence of vomiting, or any considerable purging; and nothing was more common, a few years since, than the administration of from twelve grains to a drachm daily, in divided doses of one, two, or three grains, with no effect of the kind after the first day or two. Sometimes, by giving a grain every hour or two, and gradually increasing, the medicine has been augmented to the quantities mentioned without vomiting at all. in general, however, there are at first vomiting and purging, which may continue more or less for twelve hours, a whole day, or at most two or three days, after which the stomach appears to become tolerant, and bears the medicine without suffering, or even inconvenience. in genera], tolerance is established on the second day, or earlier. it is true that it has usually been in highly inflammatory diseases that these large quantities have been administered; and it has been thought that the state of system, under these circumstances, might offer a peculiar resistance to the ordinary nauseating influence of the antimonial, not to be expected in health. This is probably the case to some extent. But similar doses have also been given in affections unattended with fever, and with similar results; and the probability is that this peculiarity of action is physiological, and applicable in health as in disease. Nor is it very difficult of explanation. I have before said that, though the state of nausea is very depressing, yet the sedative influence of the antimonial over the circulation may occur independently of this condition. The two may coincide, and the general effect may thus be increased; but they may exist wholly independently of each other. indeed, the peculiar depressing effects of the antimonial, upon which its therapeutic virtues mainly depend, are often not experienced when it vomits and purges actively, for the very obvious reason that it is either removed from the system, or fails of being absorbed in consequence of the irritated state of the membrane. Now, nausea and vomiting are not dependent on the simple action of the medicine on the stomach. if the connection between this and the nervous centres be cut off, neither is the sensation of nausea felt, nor the emetic effect experienced. it is, therefore, upon the impression made on the organic nervous centres connected with the stomach, that the medicine depends for its nauseating operation. But, as the nervous centres of animal life rapidly become accustomed to impressions upon them, the same is probably true, though in a less degree, of the organic. The dose of the emetic medicine, which at first produced nausea, has consequently less and less of this effect upon repetition; so that in time, as in the case of the narcotics, it may be carried to an almost unlimited extent, in relation to this effect alone. The positive limits must be determined by the capacity of the living tissue to bear the chemical influence of the medicine, which, in the case of tartar emetic, might, if certain quantities are exceeded, lead to serious organic results. But, while the nervous centres, which are the proper seat of the sense of nausea, and the source whence flow all its peculiar influences, become insensible to the action of the antimonial on the stomach, it still exerts its sedative influence, through absorption, upon the circulation and respiration, which are often greatly reduced. Thus, the pulse may fall in a few days from the natural standard of between seventy and eighty, down to between forty and fifty, and afterwards be long maintained at the lower rate; though M. Trousseau states that it is rarely diminished more than one-fifth or one-quarter of the number of its beats. it is at the same time sensibly weakened. The respiration is lowered even in a greater ratio than the pulse. The same author informs us that he has known it to fall from twenty and twenty-four times in a minute to six. (Traite de Thérap., 4e ed., II. 699.) it is singular that, under these circumstances of great circulatory and respiratory depression, the mind is wholly unaffected, the muscles retain their strength, and the organic functions, with the exception of the two referred to, appear not to suffer. Thus it is seen that this condition differs, toto coelo; from that induced by nausea. Sometimes, instead of being reduced regularly, the pulse becomes first irregular and intermittent under the use of the medicine; and I have noticed the same thing in reference to digitalis.