Thus, no one disease, properly so called, can, with the slightest truth, be said to fall under three different classes, as inflammatory and suppurative phthysis, which are even commonly reckoned distinct stages, or as fracture, inflammation, &c. which are essentially different in their nature and may actually be combined in every possible form. Thus it can serve no useful purpose to reckon them one disease, while it destroys every natural arrangement and all the invaluable consequences dependent on it, and absolutely leads first to confusion, next to false reasoning and then to the most fatal errors in actual practice. Although, however, nosology must thus, in any thing like a natural arrangement, be fixed most accurately upon the basis of physiology, the classification of every disease may be derived from the particular derangement of that individual function which occasions the derangement of all the rest, and not from the derangement of all the three functions which would render names uselessly complex.—I say uselessly, because, as the whole of any one disease, commonly so termed, is primarily dependent on the derangement of one function, so health is to be recovered chiefly by the restoration of that function, and the mode of cure is chiefly indicated by the name of genus under which the disease is _primarily_ arranged. This last is one of the most important consequences of such a system. If, however, the names of diseases and their classification are not thus made dependent most strictly on each specific change from the healthy state described in physiology, they are at once arbitrary and unnatural; the pathology and nosology of which they constitute a part, have not their foundation in physiology, nor is the practice constructed upon them indicated by the reasonings it delivers. To reckon a series of occurrences which entirely differ in their nature, consequences and mode of cure, as one disease, may serve the purposes of common language, but by no means those of medical science and medical arrangement. In considering the natural arrangement of medical science exhibited above, it will be particularly necessary to avoid substituting the term “organ” for “function.” The term “diseases of organs” expresses merely the seats of disease, whilst the term “diseases of functions” expresses their nature. Nevertheless a reference may also be made to the various organs, as it is evident that there may be disease of the vital or any other function in a mechanical organ. Thus a tumour in a bone is a disease of secretion, or an ulcer in a similar situation a disease of absorption; both being orders of the class—Diseases of the vital functions.