That the _uric acid theory_ should more than any other have found ready acceptance, is not so much to be wondered at. The one solitary pathological fact that emerged out of the mist of hypotheses was that established by Garrod, viz., the _excess of uric acid in the blood_. It survived and still survives the corroding test of time. Surely such must be the _fons et origo mali_, and how obtrusive _the uratic deposits_, so ready to hand, objective affirmations of the truth of their contention. This apparent simplicity how delusive! yet not wholly unprofitable. For if in these latter days our knowledge of the life-history of _uric acid_ and _purin bodies_ in the organism has evolved from “a state of chaos and guesswork to one of system and scientific accuracy,” the seeds thereof were sown by these hardy pioneers, their, to us crude, researches in the dark regions of bio-chemistry. Here it would appear opportune to outline our plan of procedure in approaching this abstruse subject—_gout_. In the coming chapter we shall attempt to define and classify the various types of the disorder before passing on to discuss its _etiology_ and _morbid anatomy_. Now all will agree that the more recent revelations of _chemical physiology_ and _chemical pathology_ have an intimate bearing on the problem to be considered. We shall therefore, before proceeding to the more purely _clinical_ aspects of the disease, deal with the modern conceptions of _protein_ and _purin metabolism_, more especially the latter. Subsequently our scrutiny will be narrowed to consideration of the _chemical_ structure of _uric acid_, its solubility, sources, mode of formation and destruction. In possession of these facts the relationship of uric acid to gout will be dealt with, in regard to respectively _uric acid excretion_, _uricæmia_, and _uratosis_. The inadequacy of the uric acid theory of the causation of gout will then be discussed and the possible intrusion of an _infective_ element in its genesis advocated. This accomplished, we shall proceed to the section dealing with the clinical aspects of the disorder, its _regular_ and so-called _irregular_ manifestations. Thence we shall proceed to the diagnosis of gout, while the terminal chapter will be devoted to that all-important subject—the prophylaxis and treatment of the affection. CHAPTER IV DEFINITION, CLASSIFICATION, ETIOLOGY, AND MORBID ANATOMY DEFINITION AND CLASSIFICATION Said Locke long since, “There are some words which will not be defined,” and surely of these is gout; for reflection upon the proffered definitions thereof is apt to leave one with the depressing impression that the disorder is both “incomprehensible and infinite.”