Inflammation has been variously defined as “perverted nutrition,” as a “protective reaction of the organism against irritant agents” and in other terms that express at once too much and too little, without actually defining the morbid process. Older definitions dealt with the manifest disorders of circulation, of innervation or of tissue change too often exalting the importance of one set of changes at the expense of another and thus giving in the main a one sided view of the morbid process. Some modern bacteriologists are inclined to refuse the title to any morbid process that is not caused by the presence of microbes or their toxic products. To them the changes occurring in an aseptic wound or in a simple fracture in process of healing are purely reparatory and partake no more of the nature of inflammation than do the developmental changes in the growing embryo. While to a large extent true, this exclusive view implies exceptions, since if the chemical poisons derived from the bacteria can develop inflammation, the same must be admitted as possible for chemical irritants drawn from other sources. As a matter of fact inflammation, occurring as it does in very different tissues, vascular and nonvascular, fibrous, cellular, parenchymatous, etc., and in connection with a great variety of irritants, must be held to include a large group of morbid processes, bearing to each other a strong family relationship and resemblance, and yet differing in many important details. Each irritant (heat, cold, electricity, chemical irritant, incised, punctured, lacerated or contused wound, rupture, fracture, foreign body, parasite, microbe, toxin, etc.,) has its own special character and mode of irritation; each tissue has its own special method of succumbing or reacting and its own amount of blood supply; and each system and organ has its own native or acquired power of resistance and reaction. Inflammation agrees with active hyperæmia in the tendency to dilation of the vessels and an increased flow of blood to the part or if the irritated part is nonvascular like the cornea or articular cartilage, then to the parts adjacent. It differs, however, in the more active cell proliferation, and in the nature of the liquid transudation which is richer in albumen fibrine, cells and phosphates. Abstractly the inflamed part retains very active vital processes, trophic and exudative, but these, are largely changed from the normal and are, it is claimed, perverted, yet they preside over the processes of cell growth and decay, the removal of injured or useless tissue, and later, over the building up of new material, and repair of loss. Active hyperæmia on the other hand is mainly a circulatory disorder, and when it advances so as to determine changes in the cells and tissues it is held to have merged into inflammation.