In this connexion I will make a remark or two upon a subject which is often the topic of conversation in common as well as professional circles, viz., the modus operandi of medicines, or the mode by which they cure disease. It is a common, but a very erroneous idea, that this subject is easily understood, and much reproach is cast upon physicians for their differences of opinion in relation to it. The modus operandi of many remedies is, as I have already said, wholly unknown, and the knowledge which we have of it in any case is more or less imperfect. And after all, though it may gratify curiosity to know _how_ a medicine cures disease, it is comparatively a matter of little importance. The fact that it does so is the material fact. The knowledge, which it is practically important to obtain in relation to any remedy, is a knowledge of its effects, and of the circumstances which modify them. And physicians, however much they may speculate about the modus operandi of medicines, commonly view this subject in this practical light at the bedside of the sick. The question whether opium is essentially a sedative or a stimulant is forgotten, when a patient suffering the tortures of spasmodic colic is to be relieved. The material fact is, that it can relieve the pain—_how_ it will do it is not just then a subject of consideration. A reform is now in progress in the medical profession. The struggle to break loose from theory is fairly begun. A deep consciousness, that the science of medicine is cumbered by a mass of rubbish, has awakened a disposition to a more careful and rigid observation. The _Materia Medica_ of the profession is especially burdened in this way. The virtues which are attributed to a large portion of the remedies in use require to be tested in order to strip the statements which are made in regard to them of all that is inaccurate and false. Much of the positive medication of the present day will probably be proved by the tests of a rigid observation to be _aimless_, but by no means harmless. The over-dosing, which has been so much in vogue both with the community and the profession, is already fast losing its popularity. Heretofore the great object of the physician has been to do _positive good_ to the patient—to overcome disease by a well-directed onset of _heroic_ remedies—and it has been a secondary object altogether to guard against doing him harm. But medical practice is becoming reversed in this respect. It may at the present time be said of quite a large proportion of the profession, that it is the principal object of the physician to avoid doing harm to the patient, and to prevent harm from being done to him by himself and by his friends: and then, after looking well to this object, he is ready to do whatever positive good he sees can be done in the case. Accordingly, cautionary and quieting measures, intended to remove the obstacles which may hinder the operation of the curative power