_The first part of the lecture is the substance of an essay which was read by the author before the Royal Medical Society of Edinburgh, intended as a defence of the general principles of the system of Dr. Brown, whose pupil he then was. It was, according to custom, transcribed into the books of the society, and the public have now an opportunity of judging how far Dr. Girtanner, in his first essay published in the Journal de Physique, about two years after, in which he gives the theory as his own, without the least acknowledgment to the much injured and unfortunate author of the_ Elementa Medicinae, _has borrowed from this essay._ _In public lectures, novelty is not to be expected, the principal object of the lecturer being to place in a proper point of view, what has been before discovered. The author has therefore freely availed himself of the labours of others, particularly of the popular publications of Dr. Beddoes, which he takes this opportunity of acknowledging._ _This lecture is published almost_ verbatim _as it was delivered. On this account the experiments mentioned are not minutely described, the reader being supposed to see them performed._ * * * * * A LECTURE, &c. THE greatest blessing we enjoy is health, without it, wealth, honors, and every other consideration, would be insipid, and even irksome; the preservation of this state therefore, naturally concerns us all. In this lecture, I shall not attempt to teach you to become your own physicians, for when the barriers of health are once broken down, and disease has established itself, it requires the deepest attention, and an accurate acquaintance with the extensive science of medicine, to combat it; to attain this knowledge demands the labour of years. But, a majority of the diseases to which we are subject, are the effects of our own ignorance or imprudence, and it is often very easy to prevent them; mere precepts however, have seldom much effect, unless the reasoning upon them be rendered evident; on this account, I shall first endeavour, in as plain and easy a manner as possible, to explain to you the laws by which life is governed; and when we see in what health consists, we shall be better enabled to take such methods as may preserve it. Health is the easy and pleasant exercise of all the functions of the body and mind; and disease consists in the uneasy and disproportioned exercise of all, or some of the functions.