portant questions wholly unresolved; - such is the difficulty of obtaining unequivocal proofs of nature essential to a just theory. The same with respect to the true doctrine of inflammation; a question which spreads itself, directly or indirectly, over every part of pathology. Here the most various and refined inquiries, aided by the highest powers of the microscope, have not yet made it certain whether there be an increased or diminished action of the capillaries of the inflamed part; or in what mere turgescence differs from inflammation.*

The history of contagious diseases furnishes another instance scarcely less remarkable. It is the common belief, and one plausible enough in its first aspect, that the laws of contagion are simple and readily learnt. No mistake can be greater than this. All parts of the subject, even the circumstances most essential to practice, are wrapt up in doubt; and the evidence is of so intricate a kind, and so much disturbed by seeming exceptions, that the best judgments are perpetually at fault upon it. The same remark may be extended to other classes of diseases, where time and the most acute observation have hitherto failed to extricate truth from the multitude of conditions present; but where, nevertheless, we have the certainty of relations hitherto undetermined, the fixing of which belongs to future research, and will well repay it in the result.

The observations just made are not less true in relation to the various remedies we employ, even those most familiar, and seemingly simplest in use. The difficulties already noticed as belonging to the evidence of their effects, extend yet further, and more remarkably, to the theory of their action;

*The active renewal of controversy on these points among modern writers shows at once their importance, and the incompleteness of the knowledge yet obtained on the subject.

and our knowledge has scarcely yet passed the threshold of this inquiry.

It must be admitted, however, that the methods of research in medicine at the present time have gained greatly in exactness, and the just appreciation of facts, upon those of any previous period:-a natural effect of increasing exactness in all other branches of science. A very especial advantage here has been the application of numerical methods and averages to the history of disease; thereby giving it the same course and certainty of result which belong to statistical inquiry on other subjects. Averages may in some sort be termed the mathematics of medical science. It is obvious, indeed, that the value of inferences thus obtained, depends on the exact estimate of what are the same facts,—what merely connected by resemblance or partial analogy. Pathological results, essentially different, may be classed together by inexact observers, or by separate observers under different views. These, however, are errors incident to every human pursuit, and best corrected by numerous and repeated averages. The principle in question is indeed singularly effectual in obviating the difficulties of evidence already noticed; and the success with which it has been employed of late, by many eminent observers, affords assurance of the results that may hereafter be expected from this source. Through medical statistics lies the most secure path into the philosophy of medicine.*

* The inquiries which so greatly distinguish M. Louis as a pathologist, may be noted as eminent examples of this method, which is now pursued with great success by many physicians in our own country. The materials furnished for it, under the new Registration Act, are of the most valuable kind; and the volume lately published, as the first Annual Report of the Registrar-General, prefaced by Mr. Farr's letter on the classification of these materials, gives full proof of what will be effected for medical science by such a system, so conducted. The same remark applies to the Statistical

In looking further to the chance of overcoming these difficulties in the future, regard must be had to the principle, now verified in so many cases, that in proportion to the complexity of phenomena, is augmented also the number of relations in which they may be surveyed and made the subjects of experiment.* The application of this principle to medical science is every day becoming more apparent. Each new path of physical knowledge opened, each single fact discovered, has given guidance more or less direct towards the objects still unattained in physiology and the treatment of disease. The unexpectedness of some of the relations, thus determined and converted to use, is the best augury for further advances in this direction of pursuit.

A due estimate among medical men themselves of the nature of the proofs with which they have to deal is now more especially needful, when the older doctrines of physic and physiology are all undergoing the revision required by modern science; and when new medicinal agents are every day produced upon trial, many of them dangerously active in their effects, many suggested by analogies which need to be verified by the most cautious experience. Hasty and imprudent belief may here become a cause of serious mischief; the wider in its spread, as the minds most prone to this credulity are those most ready also to publish to the world their premature conclusions; and thus to mislead the many who

Reports of the sickness and mortality in the British army on the different Colonial stations, as presented to parliament, and lately published. Besides many other important results, these Reports correct errors which have long existed as to some particular relations between climate and disease.

* M. Comte, in his "Cours de Philosophie Positive," has defined this as a general law, through which compensation is made for the difficulty or impossibility of giving a mathematical form to certain branches of physics; such particularly as relate to the phenomena of organic bodies.

found their own practice upon faith in others; or who seek after novelty, as if this were in itself an incontestable good.

It must, however, be added, that on questions of medical evidence there may be an excess of scepticism as well as of credulity. Sometimes this occurs in effect of a temperament of mind (not uncommon among thinking men) which is disposed to see all things under doubt and distrust. There are other cases, where the same feeling, not originally present, grows upon the mind of physicians who have been too deeply immersed in the details of practice. The hurried passage from one patient to another precludes that close observation, which alone can justify, except under especial circumstances, the use of new remedies or active methods of treatment. From conscience, as well as convenience, they come to confine themselves to what is safe, or absolutely necessary; and thus is engendered by degrees a distrust of all that lies beyond this limit.

Though such scepticism be less dangerous than a rash and hasty belief, it is manifestly hurtful in practice, and an unjust estimate of medicine as a science; both as it now exists, and as it is capable of being extended and improved. No one can reasonably doubt that we have means in our hands, admitting of being turned to large account of good or ill. Neither would it be reasonable to distrust the knowledge gained from a faithful experience as to the manner of using these means, and others which may hereafter become known to us, safely and beneficially for the relief of disease. It is clear that between the two extremes just noticed, there is a middle course, which men of sound sense will perceive; and to which they alone can steadily adhere, amidst the many difficulties besetting at once the judgment and the conduct of the physician.

I am the rather led to these remarks on the nature of

medical evidence, and the causes moral as well as physical affecting it, looking at the wonderful advances which have been made in all other branches of science; not by the addition of new facts only, but even yet more by new methods and instruments of research, and increasing exactness of details in every point of inquiry. The dissimilarity of the proofs, and the greater difficulty of their certain attainment, must ever keep practical medicine in the rear of other sciences. But its still wider scope of usefulness requires that the distance should be abridged as far as possible; and that no occasion should be lost,—by improved methods as well as by new facts,-by more cautious observation, and greater exactness of testimony,—of maintaining its fit place among the other great objects of human knowledge.