The Action of Medicines in the System. Frederick William Headland
surrounding an inquiry into the modus operandi of medicines, because it will be some excuse for the manifest insufficiency of the sketch which I am about to draw. For this, too, I may find a further apology in the fallacies and mistakes, both of reasoning and statement, of which previous writers have been guilty. These are best shown by their discrepancies. On no question, perhaps, have scientific men differed more than on the theory of the action of medicines. Either facts essentially opposed and incompatible have been adduced by the disagreeing parties; or, which is nearly as common, the same fact has received two distinct and opposite interpretations. Many hypotheses, when tested, are seen to be grounded on bare assertions, and to be destitute of logical proof; many others are attempted to be established on ill-sustained analogies. Analogy, in such a case as this, may be used to increase a probability already evidenced; but by itself it is no proof, for we find often that medicines are capable of producing the same result in very dissimilar ways.
How then are we to arrive at the truth! The best and surest way is to be extremely careful in the means which we employ in its discovery.
It is, I think, impossible to overrate the importance of exact precision of language and thought in scientific details, and in the deduction of conclusions from them.[4] A subject so interesting as this requires to be treated in a logical way. Facts, when ascertained, should be ranged together and compared, and exact inferences made, without ever straining a point. And when we are inclined to hazard a theory that is barely supported, we should take care to state it as a theory, and not to bring it forward as a truth. It has not been an uncommon habit among scientific authors, who should be of all men the most careful and exact, to confound assertion with fact—to mistake hypothesis for truth. In such illogical and incorrect reasoning is to be found the true source of a multitude of errors.
Being sensible of this danger, I have endeavoured to keep it in view in the arrangement of this Essay. In order to obtain, if possible, this clearness and precision, or at all events, to be better understood, I have arranged the heads of my ideas on the action of medicines in a number of distinct propositions, the scope of which will be presently described. I shall attempt to prove each of them separately, as if it were a theorem in geometry, sometimes dividing it first into a number of minor propositions, which, taken together, imply the original one, and which have to be severally discussed.
The great use of such an arrangement is its distinctness: so that it may in any case be easily seen whether a proposition has been established, or whether I have failed to prove it. These propositions are the foundation of the Essay; and upon them has been erected a superstructure of more or less logical consistency. In them has been stated about as much of the general principles by which medicines operate as seems to me to be capable of distinct proof: i.e. which may be regarded with that kind of certainty which we generally expect to attain to in scientific matters. So far, then, I have kept myself in a straight road, between two walls, diverging neither to the right nor to the left to gratify my inclination; it being, as I have said, a most obvious duty to guard against stating that for fact which is at the best uncertain. But having gone so far, I have in several instances indulged in speculations and hypotheses on certain matters, taking care to state that such explanations are only probable, and very far from determined. But it is often our duty to inquire into uncertain things; and those who do so, who officiate, in however humble a capacity, as the pioneers of knowledge, have to hazard many conjectures before they arrive at the truth. In striving after truth, we must investigate many an unknown path, and try at many a door where we have not before entered. Thus, when in some cases I have perceived before me a line of thought stretching onwards, and seeming to lead somewhere in the direction of truth, I have not, as it were, shunned it, or turned aside to tread only in more certain paths, but I have thought it my duty to follow it up, and to investigate it thoroughly, to see if by any means it might not help me on my way to that desired haven. These theories are the weak points of the Essay, but I must crave indulgence for them on the grounds alleged above. It will be observed that the original propositions are so stated, that the overthrow of any one of these extra hypotheses would not shake them, or in any way invalidate their proof.
I will now sketch out the arrangement which I propose to follow in the consideration of the topics which present themselves to me.
In the next chapter I shall take a brief review of the opinions of other writers on the subject of the action of medicines; knowing, indeed, that in so short a notice I shall be perfectly unable to do them justice, but wishing, in some broad points, to draw the line between what is known and what is unknown—what is ascertained and what is debated—what is approved and what condemned. In some cases also I may venture to object to opinions hitherto unquestioned. Now, as the best key to the main opinions of authors on this subject, we have to consider the various classifications of medicines which they have adopted. A classification of remedies presupposes a set of theories concerning either their primary action or their general results, and is, in fact, identical with them. The formation of such an arrangement depends on the necessity of considering medicines in groups, each possessed of some common character, in order that their various properties may be simplified, and admit of being compared.
In a classification we do not so much consider the peculiarities of single remedies, as the points in which large numbers agree together. These points of resemblance we gene rally find to be of the most importance. I have to consider three sets of authors in the second chapter. The first set treat of the general or ultimate effect of a medicine on the system; and classify medicines accordingly. A second set of writers have arranged therapeutical agents according to the organ or part of the body to which their action is especially directed. Neither of these deal with the mode in which medicines act as the basis of classification. A third set of writers have attempted in various ways to explain the modes of operation of medicines. They have laid down general rules about these operations, and have constructed more or less plausible theories on the subject. Some few have classified remedies on this plan. Now, with these theories I am more particularly concerned, as they trench immediately on the subject of this Essay. But they are not many, and it will not take us long to review them.
It is easier to find fault than to teach. After pointing out the shortcomings of some who have preceded me, I find myself necessitated in the third chapter to state my own conclusions as to the modus operandi of medicines.
Let us consider, as it were, the history of a remedy from the beginning to the end of its course. It is already "introduced into the stomach"—we must commence with it there. Now it does not remain there. It cannot act from the surface of the stomach through the medium of the nervous system.
In the First Proposition it is affirmed that it must obtain entry into the fluids of the body—pass, that is, from the intestinal canal into the system at large—before its action can begin. There are four proofs of this. It is shown that when introduced at another part of the body a medicine acts in the same way as when placed in the stomach. It is found by direct experiment that a poison will not act through the medium of nerves only, but that its passage in the blood is required. Thirdly, the course of the circulation is quick enough for the most rapid poison or medicine to pass quite round the body from the veins of the stomach before it begins to operate. The last and most conclusive argument to show that medicines pass out of the stomach into the system, is that they have actually been detected by chemists, not only in the blood, but in the secretions formed from the blood. Remedies, then, pass from the stomach into the blood and fluids. How do they do so?
In the Second Proposition it is laid down that all those which are soluble in water, or in the secretions of the stomach or intestines, pass through the coats of these organs into the interior of the capillary veins which surround them. It has already been shown that most medicines pass through in some way; we shall now have to learn how they pass, and what special arrangements are made for the passage of substances differing in nature. By the physical process of absorption a liquid may pass through the animal membranes, from the interior of the stomach or intestine to the interior of the small vein which lies close outside it. In examining the laws by which this process is conducted, we shall find that all the requirements are present in these parts, provided only that the substance to be absorbed shall be first in some way dissolved, and reduced to the liquid state. In the stomach there is, in contact with the substance just introduced, a thin watery