The Action of Medicines in the System / Or, on the mode in which therapeutic agents introduced into the stomach produce their peculiar effects on the animal economy

by Frederick William Headland

Frictions and Sinapisms act on the skin externally on this principle. So do Blisters and Issues; but they are not simply counter-irritants, for they also drain away the serum of the blood. It is not now within my province to consider such an action on the skin, any further than for the purpose of stating that similar local impressions on the mucous surface of the stomach and intestines are capable of operating on the same principle.

We have then to consider what are the local actions that medicines are capable of producing on these surfaces.

And first, it must be laid down as a rule, that all medicines, when given in excess, act as irritants on the stomach and intestines. This is more especially the case with mineral salts, with the bitter and astringent principles of vegetables, and with acrid and resinous matters. By irritating the stomach locally, they cause vomiting; by causing peristaltic action of the bowels, purging. Some of them are actually employed to produce these effects, and will be presently specified.

The corrosive and narcotico-acrid poisons may produce by this local action a degree of irritation sufficient to cause death. In the case of the first, some erosion of the mucous surface may occur. By both kinds violent vomiting and purging is apt to be produced, and succeeded by symptoms of collapse. These last, however, are not therapeutic agents, when in such doses.

Antidotes, employed to counteract these poisons, are remedies which are given to act locally in extraordinary cases. There are three chief kinds of them; Demulcents, to sheath the irritated surface, and protect it from further injury; Emetics and Purgatives, to get rid of the poison; and chemical antidotes, to neutralize it or render it insoluble while in the stomach. With this last object, acids are given in alkaline, and alkalies in acid poisoning. The soluble salts of Lead may be precipitated and rendered insoluble by sulphuric acid or sulphates. Those of Mercury, Copper, and Zinc, by albumen. Tannic acid precipitates the vegetable alkaloids. There are some other special antidotes of the same kind.

Let us now consider the three kinds of remedial agents in ordinary use, which are employed for the purpose of producing a local effect on the mucous surfaces, before absorption, or without absorption.

a. Irritant emetics.—Two kinds of medicines are employed to produce Vomiting,—specific emetics, and irritant emetics. The former act from the blood; the latter, by local irritation. In the same way that irritation of the external surface of the body will sometimes cause at the same time the direct contraction of a neighbouring muscle, and the reflex contraction of others at a distance, so does local irritation operate on the surface of the stomach. On the one hand the muscle of the stomach itself is caused to contract, so that, the pylorus being at the same time forcibly closed, it tends to expel its contents in the wrong direction. On the other hand, a large set of distant muscles is thrown into sudden action. First, a quick deep breath is taken by means of the inspiratory muscles. Then the aperture of the glottis is spasmodically closed, so that, the lungs being full, the diaphragm cannot be pushed upwards. Then immediately the abdominal muscles contract, and being unable to act on the diaphragm, they press on the stomach, emptying it forcibly of its contents.

All this is by reflex action, and follows sympathetically the contractions of the stomach, co-operating with it, and resulting, like it, from irritation of the sensitive mucous surface.[27] Such is the action of an irritant emetic.

Now, Tartar Emetic and Ipecacuanha do not act in this way. When injected into the blood elsewhere, in sufficient quantity, they are found to produce vomiting. They have also special actions on the heart and lungs, which are not possessed by merely irritant emetics. They seem to me to act specifically on the Vagus Nerve, which is supplied to these organs as well as to the stomach, and to cause vomiting by deranging its functions. By this action on the Vagus while in the blood, they excite, in a special way, the same reflex contractions which are produced, in the case of an irritant emetic, by irritation of the extremity of that nerve in the mucous membrane. They are thus Neurotics, or nerve-medicines. They are not gland-medicines; or, at least, there is no proof that they are excreted by the stomach, and thus they do not come under my definition of Eliminatives. All substances which touch the surface of the stomach cause it to pour out its secretion.

Specific emetics cause nausea, even without vomiting, depressing the action of the heart by their influence over the Vagus nerve. Irritant emetics scarcely cause nausea, producing only a feeling of discomfort, arising from the inverted action of the stomach.