A medicine may have multiple influences on the system, brought about by different modifying circumstances, but at the same time it may have a distinctive dual action, independent of any chemical or physiological interference. Instead of having an elective force on one organ, it will act with equal energy on two. For illustration we will give a few examples. Squills addresses itself to the kidneys, as well as to the lungs and acts simultaneously both as a diuretic and expectorant. Digitalis follows the same law, and splits up its force. one part to act on the heart and the other on the kidneys. Sweet spirits of nitre acts at the same time on the skin and kidneys as diaphoretic and diuretic. The dual action of belladonna is ostensibly manifested on the eye as a mydriatic, and as a suppressor of the secretions, causing dryness of the throat both operations brought about primarily through the excito-motor influence of the drug. Duboi-sia, although an efficient substitute for atropia, has a less dual character, being more powerful in its mydriatic action, but less irritating to the mucous membrane.

All nauseants appear to have a simultaneous triple action, namely: nauseant, expectorant and diaphoretic. This is the best that can be done at one time with ipecac, although it has other collateral curative properties, as a tonic in dyspepsia, as a stomachic sedative in nausea, as an alterative in diarrhoea and defective assimilation, and as an outdoor diuretic, etc. Yet, strictly speaking, we hardly can assign a triple character to nauseants when we join the physiological operation of diaphoresis and expectoration, and make it one general process of exosmosis. It appears what is a diaphoretic is more or less an expectorant, and vice versa, that is, if the excretory flow is turned off from the kidneys by confining the body in a warm place. The question is one of great diagnostic importance, in particular in the initiatory stage of a pulmonary disease. To lay your hand on the skin, and by the degree of its temperature and moisture diagnose a pulmonary hyperaemia, is by no means an impossibility. But to practice such artistic skill in diagnosis, we must mark the difference between a physiological and pathological perspiration. The asthenic perspiration of a chronic disease would hold no exact relation to the organic trouble that may exist. There is, evidently, a law that governs the operations of the lungs and skin, not as organs of aeration alone, but as performing their functions under the influence of atmospheric air.*

*Gubler.

Nux vomica has two very distinctive properties; constitutionally, as a powerful excitant of the cerebro-spinal system; locally, somewhat like cocaine, as a local anaesthesia - a dual action, but of a decided antagonistic character. This antagonistic dual action we find in opium as a stimulant narcotic - its effects on the iris alone betray the powerful internal tension it produces, which at the same time may be masked by a state of insensibility. In the case of tartar emetic given internally, vomiting occurs in consequence of the irritation of the mucous lining of the stomach, but the drug through its direct effect on the cardiac tissue, causes at the same time reduction in the force of the heart's action.

When chloroform is given by inhalation we have a direct action on the cerebro-spinal nerve centres, particularly on the cerebrum, at the same time we have a checking of the heart's action through reflex action aroused by local contact of the drug with the mucous lining of the air passages. †

It is sometimes necessary in practice to annul the dual action of a remedy by synergistic means, where it is desirable to have but one organ acted upon. Thus, bicarbonate of soda joined with calomel, results in nothing more than an alterative cathartic. Digitalis, as already stated, will affect either the heart or the kidneys, according to the nature of the solvent. Turpentine affects both the intestines and kidneys, but an adjuvant of castor oil will confine its action to the bowels, with little or no communication with the kidneys. A reverse action could be effected by suspending the peristaltic intestinal canal. This may sometimes be resorted to with advantage in puerpural paralysis of the sphincter vesicas,‡ nevertheless, running the imminent risk of inflicting a serious damage upon the urinary organs.

We are led to the inquiry of the ultimate tendency of this medical dual action. Where lies the force to split up a drug in two, assigning each part to two different organs, in which each performs a function of its own? To solve the question, we have first to learn what class of remedies possess these characteristics. These are nearly all medicines of a high power, and without this physiological division many of them would become toxic in the extreme. Therefore, it is a protective measure on the part of the economy when receiving drugs of this class. Arsenic is strictly a dual drug, at least up to its point of cumulative action.

*On the relation of Atmospheric Air to the Human Body; by Dr. G. P. Hachenberg, Western Lancet, (Cin., O.) Oct., 1854.

†Dr. L. Lewin.

‡Prof. Gunning Bedford.