Although the practitioner may not be able to satisfy his ethical desire to explain the action of preparations of iodine in the latter class of pathological conditions, he soon makes the discovery that these actions and results are, to a very considerable degree, dependent upon more or less well-marked clinical and physical phenomena. In order to be able to give to his use of iodine, in its various forms, even a semblance of ethical practice, and, also, in order to be able to roughly classify and select the conditions in which he may use iodine with some expectation of uniform results, it becomes imperative that the practitioner acquaint himself with these facts and phenomena. Not only this, but he must acquaint himself, as well, with the peculiar and individual effects and actions, in a clinical sense, of the different forms in which iodine is used as a topical or regional application. What may be an indication for the use of iodine in one form, may lack the requisite pathological status for its application in a successful manner in one of its other forms. Thus, in a given pathological condition, an ointment of iodine may fall far short of the therapeutic power that the practitioner expects it to exert, despite the fact that the case is clearly one for iodine therapy. When, on the other hand, in the same case, use is made of the tincture of iodine, or of an aqueous solution of iodine, the desired results may be obtained with almost amazing promptness. Again, in another class of cases, the reverse may be true. Although, in a goodly proportion of the cases to be discussed in the following chapters in this treatise, the practitioner must come into direct and frequent clinical contact with the pathological conditions themselves in order to become thoroughly acquainted with the clinical and physical facts referred to, he will derive much benefit from a careful reading of these chapters, to the extent that he will note not only new lines of thought with regard to iodine medication, but he may also lay, in their reading, the foundation for an ethical system of iodine therapy in so far as this is possible in the light of our present acquaintance with the subject. III. Special Considerations of Local Iodine Therapy. When we undertake the consideration of those features of iodine therapy which have to do with its adaptability to definite remedial ends, we enter upon a field of thought that may take several forms.