therefore, as soon as I was employed to teach a more complete system of the practice of physic, I judged it necessary to publish a text-book, not only for the benefit of my hearers, but that I might also have an opportunity of obtaining the opinion of the public more at large, and thereby be enabled either to vindicate my doctrines, or be taught to correct them. These were the motives for my attempting the volumes I formerly published; and now, from many years experience of their utility to my hearers, as well as from the favourable reception they have met with from the public, I am induced to give a new edition of this work, not only, as I hope, more correct in many parts, but also more complete and comprehensive in its general extent.

At the first publication of this work, it was intended chiefly for the use of those gentlemen who attended my lectures; although, even then, for the reasons I have mentioned, it was rendered more full than text-books commonly are; and, in the repeated editions I have since had occasion to give, I have been constantly endeavouring to ren der it more full and comprehensive. In these respects, I hope the present edition will appear to be rendered more fit for general use, and better calculated to afford satisfaction to all those who think they may still receive any instruction from reading on this subject.

While I thus deliver my work in its now more improved state, with the hopes that it may be of use to others, as well as to those who hear my lectures, I must, at the same time, observe, that it presents a system which is in many respects new; and therefore I apprehend it to be not only proper, but necessary, that I should explain here upon what grounds, and from what considerations, this has been attempted.

In the first place, I apprehend, that in every branch of science, with respect to which new facts are daily acquired, and these consequently giving occasion to new reflections, which correct the prin ciples formerly adopted, it is necessary, from time to time, to reform and renew the whole system, with all the additions and amendments which it has received, and is then capable of. That at present this is requisite with regard to the science of medicine, will, I believe, readily occur to every person who at all thinks for himself, and is acquainted with the systems which have hitherto prevailed. While, therefore, I attempt this, I think it may allowable, and upon this occasion even proper, that I should offer some remarks on the principal systems of medicine which have of late prevailed in Europe, and that I should take notice of the present state of physic, as it is influenced by these. Such remarks, I hope, may be of some use to those who attempt to improve their knowledge by the reading of books.

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Whether the practice of physic should admit of reasoning, or be entirely rested upon experience, has long been, and may still be, a matter of dispute. I shall not, however, at present enter upon the discussion of this, because I can venture to assert, that, at almost all times, the practice has been, and still is, with every person, founded more or less upon certain principles established by reasoning and therefore, in attempting to offer some view of the present state of physic, I must give an account of those systems of the principles of the science which have lately prevailed, or may be supposed still to prevail, in Europe.

When, after many ages of darkness, which had destroyed almost the whole of ancient literature, learning was again restored in the fifteenth century; so, from causes which are well known, it was the system of Galen alone that the physicians of those days became acquainted with; and during the course of the sixteenth century, the study of physicians was almost solely employed in explaining and confirming that system. Early, indeed, in the sixteenth century, the noted Paracelsus had laid the foundation of a chemical system, which was in direct opposition to that of Galen; and, by the efficacy of the medicines employed by Paracelsus and his followers, their system came to be received by many: but the systematic physicians continued to be chiefly Galenists, and kept

possession of the schools till the middle of the seventeenth century. It is not, however, necessary here to enter into any further detail respecting the fate of these two opposite sects; for the only circumstance concerning them, which I would wish at present to point out, is, that in the writings of both, the explanations they severally attempted to give of the phenomena of health or sickness, turned entirely upon the state of the fluids of the body.

Such was the state of the science of physic till about the middle of the seventeenth century, when the circulation of the blood came to be generally known and admitted; and when this, together with the discovery of the receptacle of the chyle, and of the thoracic duct, finally exploded the Galenic system. About the same period, a considerable revolution had taken place in the system of natural philosophy. In the course of the seventeenth century, Galileo had introduced mathematical reasoning; and Lord Bacon having proposed the method of induction, had thereby excited a disposition to observe facts, and to make experiments. These new modes of philosophizing, it might be supposed, would soon have had some influence on the state of medicine; but the progress of this was slow. The knowledge of the circulation did indeed necessarily lead to the consideration, as well as to a clearer view, of the or

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ganic system in animal bodies; which again led to the application of the mechanical philosophy towards explaining the phenomena of the animal economy; and it was applied accordingly, and continued, till very lately, to be the fashionable mode of reasoning on the subject. Such reasoning, indeed, must still, in several respects, continue to be applied; but it would be easy to shew, that it neither could, nor ever can be, applied to any great extent in explaining the animal economy; and we must therefore look for other circumstances, which had a greater share in modelling the system of physic.

With this view, it may be remarked, that, till the period just now mentioned, every physician, whether Galenist or chemist, had been so much accustomed to consider the state and condition of the fluids, both as the cause of disease, and as the foundation for explaining the operation of medicines, that what we may term an HUMORAL PATHOLOGY still continued to make a great part of every system. In these circumstances, it was soon perceived, that chemistry promised a much better explanation than the Galenic or Aristotelian philosophy had done; and therefore, while the latter was entirely laid aside, a chemical reasoning was everywhere received. Lord Bacon, with his usual sagacity, had early observed, that chemistry promised a great number of facts, and he thereby