I have now finished the consideration of the various causes of uncertainty in medical science. If I have succeeded at all in making them to be properly appreciated, the reader will agree with me when I say, that there is no science that requires higher talents for its successful investigation, and none that is so liable to wrong influences and conclusions, if the student of it be a careless and credulous observer. Notwithstanding this liability, imperatively demanding caution on the part of the physician, there has been much of careless observation in this science; and the recorded experience of the medical profession is therefore encumbered with a mass of errors. In order to get rid of these errors, and to establish the proper distinctions between the certain and the uncertain, between the true and the probable, while the merely plausible shall be entirely rejected, a judicious sifting and testing of evidence must be resorted to, credulity and skepticism both being equally avoided. FOOTNOTES: [2] The terms _chronic_ and _acute_ it may be well to define for the benefit of some of my non-professional readers. An acute disease is one which runs its course in a short time. A chronic disease, on the other hand, is one which has a long duration. For example, pneumonia, (commonly called lung fever,) is an acute disease of the lungs, while consumption is a chronic disease of the same organ. The term, acute, has reference to the violence of the symptoms of the diseases to which it is applied, rather than to their duration; while its opposite term, chronic, has reference to duration only. Use, however, has given them a technical sense which is not liable to be mistaken. [3] This subject may be found fully illustrated by Dr. Bigelow in the Annual discourse for 1835, before the Massachusetts Medical Society. CHAPTER II. SKILL IN MEDICINE. The uncertainty of medicine is often most unjustly made to give a free license to blind experimenting. It should the rather stimulate to the most careful and searching observation of all the doubtful points of the case in hand, so that whatever of experimenting may be necessary, shall be as rational and intelligent as possible. This leads me to remark, that the views, which we have taken of the uncertainty of medicine, show us in what real skill in the practice of the medical art consists. It consists in _appreciating the actual state of the patient in all respects, and then applying such remedies, and in such quantities and forms as will do the greatest probable amount of good_. This is apparently a very simple proposition. But if we consider it in all its bearings, we shall find that more is included in it than at first sight appears. I will therefore dwell on some of these points in the order in which they are suggested to my mind.