# Observations on Man (6th edition)/Part I/Chapter II/Section VIII

Section VIII
THE RELATION WHICH THE FOREGOING THEORY BEARS TO THE ART OF PHYSIC.
This proposition may appear from several hints to that purpose, which have been already given. But it will be more fully manifest, if I give a short view of the data and quæsita in the art of physic.
Now the general problem, which comprehends the whole art, is,
Having the Symptoms given, to find the Remedy.
This problem may be solved in some cases empirically and directly by the histories of distempers, and of their cures. But then there are other cases, and those not a few, to which the learning and experience of the most able physicians either cannot find histories sufficiently similar, or none where the event was successful. Hence it is necessary to attempt the solution of the general problem rationally and indirectly, by dividing it into the two following less comprehensive and consequently more manageable problems; viz.
First, Having the symptoms given, to find the deviation of the body from its natural state.
Secondly, Having this deviation given, to find the remedy.
​It is proper also to invert these two problems, and to inquire,
First, Having the deviation given, what the symptoms must be.
Secondly, Having the manner of operation of a successful remedy given, what the deviation must be.
I here use the words symptoms, deviation, and remedy, in the most general sense possible, for the sake of brevity.
Now it is very evident, that the doctrine of vibrations, or some other better doctrine, which teaches the law of action of the nervous system, has a close connexion with all these last four problems. For the nerves enter every part, as well as the blood-vessels; and the brain has as great a share in all the natural functions of the parts, and its disorders, in all their disorders, as the heart, and its disorders, can have; and much more than any other part, besides the heart.
Farther, if the doctrine of association be the necessary consequence of the doctrine of vibrations, in any such manner as I have proposed above, Prop. IX. and XI. it must have a most intimate connexion with the theory of nervous distempers, and some with that of others, on account of the just-mentioned dependence of all the parts on the brain. Or, if we separate these doctrines, still, if that of association be true, of which I suppose there is no doubt, it cannot but be of great use for explaining those distempers in which the mind is affected.
And it seems to me, that agreeably to this, the distempers of the head, spasmodic ones, the effects of poisonous bites and stings, which, as Dr. Mead justly observes, are more exerted upon the nerves than on the blood, receive much light from the doctrine of vibrations, and, in return, confirm it; and that all the disorders of the memory, fancy, and mind, do the same in respect of the doctrine of association.
I do not mean to intimate here, that the rational and indirect solution of the general problem, which comprehends the art of physic, is preferable to the empirical and direct one, where this is to be had; but only, since this cannot be had always, that we ought to proceed in an explicit and scientifical manner, rather than in a confused and popular one. For where practice is silent, physicians must and will have recourse to some theory, good or bad. And if they do not acquaint themselves with the real structure and functions of the parts, with the sensible qualities and operations of medicines, and with the most probable method of explaining both the symptoms of distempers, and the operations of medicines, they must fancy something in the place of these, and reason from such false imaginations, or perhaps from the mere agreements, oppositions, and secondary ideas, of words. The history of diseases, and their cures, is the basis of all; after this come anatomical examinations of the body, both in its natural and morbid states; and last of all, pharmacy; these three answering respectively to the general problem, and the two subordinate ones above-mentioned. And if we reason ​at all upon the functions and disorders of the parts, and the effects of medicines upon the body, so important an organ as the brain must not be left out entirely.
It may not be amiss to add here, that as all the natural functions tend to the welfare of the body, so there is a remarkable tendency in all the disorders of the body to rectify themselves. These two tendencies, taken together, make what is called nature by physicians; and the several instances of them, with their limits, dangers, ill consequences, and deviations in particular cases, deserve the highest attention from physicians, that so they may neither interrupt a favourable crisis, nor concur with a fatal one. Stahl and his followers suppose, that these tendencies arise from a rational agent presiding over the fabric of the body, and producing effects that are not subject to the laws of mechanism. But this is gratis dictum; and the plain traces of mechanism, which appear in so many instances, natural and morbid, are highly unfavourable to it. And all the evidences for the mechanical nature of the body or mind are so many encouragements to study them faithfully and diligently, since what is mechanical may both be understood and remedied.