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

It was some time ago supposed that the fæces consisted simply of those parts of the food which remained unabsorbed, and that all Purgative medicines alike acted by exciting the peristaltic motion of the bowels, and causing thus the ejection of these undigested matters. Such an opinion is now rarely maintained. Although very little is known of the separate functions of the glands of the intestinal mucous membrane, yet it is generally supposed that the fæcal matters consist in great part of excrementitious substances which are separated by their means from the blood. The excretion of fæces continues when no food is taken. It is known to go on with starving men, and with patients in fever. Liebig argues for the secretion of the greater part of the fæces, on the ground that they contain nitrogenous matters, whereas all the nitrogenous parts of the food should be absorbed for the purposes of nutrition. Thus these are probably the excreted products of changes in the system, which it is the province of the bowels to separate from the blood. (Anim. Chem. p. 156.) The odour of these matters is partly owing to sulphuretted hydrogen, or hydrosulphate of ammonia, both of which are the products of animal decomposition. On account of their presence a black colour is communicated to the fæces by the internal administration of the salts of Iron.

It seems to me to be probable that the constituents of the living as well as of the dead body are constantly subjected to the control of chemical laws, and undergoing destruction and change. Some products of these changes in an early stage are eliminated in the urine; but in great part they go on to actual putrefaction. The products of this, which are of an offensive character, are apparently discharged from the body through the follicles and glands of the intestines. We find that this decomposition is promoted and accelerated by heat, in the same way as with dead animal matter. For this reason it appears that the natives of warm climates excrete a much larger quantity of fæces than the dwellers in colder latitudes; and they are also more subject to Dysentery, Diarrhœa, and Cholera, on account of the extra work thrown upon their intestines. A similar explanation may perhaps be assigned to a curious fact noticed some time ago by Mr. Curling—viz., that acute ulceration of the duodenum is a frequent consequence of severe superficial burns. A quantity of gangrenous or decomposing matter may in such a case be carried from the surface into the circulation.

This blood-decomposition, which I suppose to be always going on, may be accelerated by the action of certain morbid poisons or processes. The secretion of the bowels is then increased, and by the excitement or over-work a diseased condition of the intestinal surface may be established. In this way the diarrhœa and ulceration of the glands in Typhoid fever may be accounted for. The air of a dissecting-room, or the neighbourhood of a noxious sewer, is apt to bring on diarrhœa by exciting a putrefaction of the blood. Severe bodily exercise, as a long walk, may cause it, by increasing the waste of tissue. We find that constipation is commonest in youth, when nutrition is most active; and diarrhœa most frequent in old age, when waste and decay go on the fastest.

When these decomposed matters which should be excreted, are retained in the blood, as is the case in constipation, they affect very injuriously both the brain and the system in general, causing torpidity of the one, and in the other favouring the progress and development of every description of morbid action. It is by cleaning such matters out of the blood, as well as by their antiphlogistic or evacuant action, that Cathartics become useful in so many diseases, and particularly in disorders of the brain. It would seem that the substances which would be eliminated by the bowels have, when retained in the blood, a peculiar action in the aggravation of disorders of this latter organ. Thus from very early times the exhibition of drastic purgatives, particularly Hellebore, has been strongly recommended in cases of mania.

But there is scarcely any disorder in which there is not, in some way or other, a deranged condition of the intestinal function, and in which, therefore, the judicious employment of purgative medicines is not at some time necessary. Either there is constipation, in which case there is a danger of the fæcal matters being retained in the blood; or there is diarrhœa, which is probably due to an over-formation of these materials in the system, and an attempt of nature at their evacuation. In each of these cases Cathartics may be necessary. The first condition is the more obstinate of the two; the second the more immediately dangerous. Some general indications for their treatment may be alluded to.

In the treatment of constipated habits it is better to keep up a constant and gentle action on the bowels than to give violent doses occasionally. A condition of this sort may sometimes co-exist with comparative health, and may then often be remedied by a slight alteration in diet, and the prescription of such kinds of food as are more relaxing in their nature than those hitherto taken. Dr. Hamilton, in his work on Purgative Medicines, states that when they are given in constipation he has found that they become more and more powerful, and may be taken in smaller and smaller doses the longer they are continued. This is probably the case with such as Castor-oil, Scammony, and Jalap, which are simply cathartic in their action. But others, such as Rhubarb and Aloes, contain a bitter and astringent matter along with the purgative principle, and though they first act upon the bowels tend for this reason in the second place to confine them. Thus while the former are best in cases of constipation, the latter are preferable in diarrhœa, as they supply us then with the very action which we require.

There are two ways, apparently opposite and inconsistent, of treating a flux from the bowels. We may try to encourage it by Purgatives; or attempt to suppress it by Astringents. Thus we may treat a common diarrhœa by Castor-oil, or by Sulphuric Acid. In dysentery we may give Calomel, or Catechu. Even in Cholera some recommend Opium, while others have employed Croton-oil. In the most obvious case, i.e. in simple diarrhœa, it is apparent that both plans are appropriate, but at different periods of the disorder. The symptom depends upon the fact of something being formed in the blood which ought to be excreted from it. Probably it is an excess of that material which is ordinarily excreted by the bowels. Its passage out by a natural effort causes at first a simple increase of the usual evacuation. It is at this time that we should give a Purgative, to favour the natural excretion, and thus, if possible, to put an end to the disturbance. But sometimes it fails to do so. The matters to be excreted are irritating, and such an excitement may be caused in the glands by their passage out, that even after this necessary secretion an inordinate and unnatural flux may be maintained. When the symptom is thus inveterate, and refuses to yield to a brisk Cathartic, it is advisable to resort to Astringents, in order to put a speedy stop to the too copious secretion. To do this in the first instance would have been wrong, except in special instances,—as in the diarrhœa which is the forerunner of cholera, when Astringents should be used from the first.

In some febrile and plethoric cases it is difficult to obtain the full action of a Purgative. This is because the absorption of the medicine is prevented by the pressure on the vascular system, and without this absorption the proper action of the Purgative cannot take place, for it has no opportunity of passing out of the blood through the glands of the bowels. In such instances it is well to combine the Cathartic with a small dose of Tartar Emetic or Ipecacuanha, which by its nauseant operation may diminish the vascular pressure, and thus favour the necessary absorption. The action of a Cathartic itself favours absorption, by draining away the fluid part of the blood, and so diminishing the tenseness of the vessels.

Ord. IV. Cholagoques.

Medicines which are thought to stimulate the action of the liver, and to promote the excretion of bile, are called Cholagogues.