48

THEORIES AND CLASSIFICATIONS.

which directly or indirectly counteract it there; that disorders, generally temporary, which depend on nervous derangement, are to be benefited by remedies which affect the nerves; and in the same way that a laxity of muscular fibre, or a failure in a secretion, should be treated by agents which especially possess the property of restoring to a right condition such parts or functions.

Concluding, then, that it is impossible to account clearly for the actions of most medicines on Mechanical or on Chemical principles, we are led to infer that their influence must for the most part be vital in its nature-that it must be such as could only be exerted in the living body. Even then we are unable to fix upon any single rule or formula which shall be capable of accounting for the actions of all at once. So it seems that the only general explanation which we can offer of the modus operandi of medicines in the cure of diseases, is to say that they operate by various counteractions.

This, then, introduces my Third Chapter.

49

CHAPTER III.

ON THE GENERAL MODES OF ACTION OF THERAPEUTIC AGENTS INTRODUCED INTO THE STOMACH.

THE principal affirmations which I have to make on this subject are divisible into Ten Propositions, as seen in the Table of Contents.

The first four of these concern the general conduct of medicines after their introduction into the stomach, and before their passage into the blood. Some broad rules are laid down by which the course which they take must be determined. The action of some few on the mucous membrane is also defined.

The remaining six Propositions treat of the subsequent behaviour of those medicines which pass into the blood and fluids of the body. Of these, the fifth specifies their general course. The sixth states that they may undergo certain changes in the system. And the concluding four treat of the various modes in which these agents may operate in the cure of disease.

The first proposition lays down the great fundamental rule of the action of medicines through the medium of the blood and fluids.

E

PROP. I. That the great majority of medicines must obtain entry into the blood, or internal fluids of the body, before their action can be manifested.*

This is to say, that the mere contact of a medicine with the stomach is not in general sufficient for the production of its peculiar action on the system. It will be seen (Prop. IV.) that the only apparent exceptions to this rule consist of agents having a mere local action on the mucous membrane, for which simple contact is all that is required.

Even when acting on any part of the system removed from this mucous surface, as when applied to the skin, it is necessary that the medicine pass away from it to enter the blood or internal fluids. In the great majority of instances it enters the blood directly. But we know that it would be sufficient for its operation if it were to enter through the chyle, or into the scrous fluid which exists in the interstices of the tissues throughout the body. For by these it might at length be conducted to distant parts. This is what is meant by internal fluids. For example, when a preparation of Aconite, or Opium, is rubbed on to the skin at any part, as soon as it has had time to penetrate the cuticle, it paralyzes the superficial sentient nerves. These are bathed in the interstitial fluid of the tissues. It is therefore very easy for the medicine to reach them without passing into the vessels at all, though when арplied in large amount it certainly tends to enter them, and may then be carried along so as to affect parts at a distance. Similarly, Belladonna, or Atropine, which, when applied to the surface of the eye or the neighbourhood of the orbit, influence the nerves of the pupil in such a manner as to cause the latter to dilate, must in all probability find a more direct road to these nerves than that which is offered by the vascular system.

*"A remedy must be absorbed, before it can exert any remote action on the animal economy."-Mialhe, L'Art de Formules.

We are not just now concerned with the way in which this passage into the blood and fluids is obtained. It is by the process of absorption. The question of passage by absorption is treated in the second and third propositions. What we have now to decide is, whether a medicine acts by mere contact with the stomach, its influence being propagated to distant parts by means of the nerves; or by passage thence into the system, acting through the medium of the blood and fluids.

I affirm that it operates in this latter way; and this is to be proved by four considerations, which we will consider in succession.

A medicine introduced into the system elsewhere acts in the same way as when introduced into the stomach.

This proves at least that contact with the mucous surface is not an essential requisite for the operation of a remedy. We may cause a medicine to be absorbed by the skin, or inject it directly into an opened vein. The result of this latter experiment proves not only that entry into a distant part of the system is sufficient for the action of a medicine, but that it will operate when introduced into the blood. Numberless proofs of this affirmation may be adduced. Tartar Emetic injected into the veins produces vomiting. A moistened leaf of Tobacco, applied over the radial artery at the wrist, has been known to produce vomiting. Sulphate of Magnesia, infused into the veins of an animal, has been found to act on the bowels.* Or let Croton Oil, or a liquid preparation of Jalap, Rhubarb, or Gamboge, be rubbed in sufficient quantity on to the abdomen, and purging will result.+ Mercurial ointment applied by friction to the skin will produce salivation. Extract of Belladonna applied to the temples causes dilatation

* By Dr. Aubert. See British and Foreign Med. Chir. Review, January, 1853.

Ascertained by Dr. Madden, and others. See Paris's Pharmacologia, 9th ed., p. 141.

of the pupil of the eye; and Tincture of Opium dropped on to the eyeball causes the pupil to contract. Ammonia inhaled as gas into the lungs will relieve fainting in the same way as when swallowed. The breathing of Prussic acid, causing its vapour to be applied to the pulmonary surface, is sufficient to kill. Prussic acid, dropped in a concentrated state into the eye of a dog, causes speedy death. Solution of Aconitina, applied to the skin, will produce numbness and tingling of distant parts. Injection of Nux Vomica, or any powerful poison, into the veins, is rapidly followed by symptoms of poisoning, like those which would have followed its introduction into the stomach. Thus contact with the stomach is not necessary, but introduction into the system anywhere is sufficient. But still, may not the poison in either case act by influencing the nerves? Even when it has entered the blood, it may not travel along in it, but act in a more direct way. So in the second part of the proof we must show that a remedy cannot act by an impression conducted from the surface of the stomach, or any other part, by means of the nerves alone.

*

The continuity of nerve is not necessary for the propagation of such effects; but vascular connection is necessary.

This alone, if established, would be sufficient to prove that a medicine must be introduced into the circulation, in order to act on distant parts. When confined to a surface, it can operate on the remote part only by its contact with the superficial extremities of the nerves. For vascular connection to be established, it must first enter the vessels. Many experiments have been made which demonstrate that the vessels are the only channel by which medicinal effects can be propagated.

M. Magendie introduced some Woorara poison into the * An exception should be made here of certain animal poisons, such as the venom of serpents, which, though they act on the system when introduced directly into the blood, seem to be rendered innocuous by the action of the stomach, which probably either decomposes them, or resists their absorption.