The nature and structure of the tissue materially modify some symptoms and exclude others, so that redness, pain and even perceptible swelling may be absent. Galen already in his time attributed the redness to an increased blood supply and the swelling to an exudation of lymph or serum, through the walls of the blood vessels: this was as near the truth as scientists arrived, until within our own time. The discoveries in this field of science have been greatly enriched in the last twenty years through the researches of the German school. Various theories have been advanced from time to time, as to the probable causes or processes that are going on in the tissues while inflammation is active. One observer believed that he had found the solution of the inquiry in a supposed spasmodic contraction of the capillary blood vessels, another in their paralysis, while still another adhered to the belief of a neurotic affection. Professor Virchow, the father of the modern school of pathological science, ascribed the conditions of the tissues to an irritable state of the inflammatory process, inducing an exaggerated cell growth; while his former pupil, Cohnheim, through an extended series of newly-devised experiments, has conclusively proved that none of the theories advanced are supported by demonstrable facts. Our present thorough knowledge of the combined disturbances and phenomena, that play their part in the vessels and tissues, of the body during the inflammatory action in living tissue is due to the unremitting toil of Professor Cohnheim. He was the first to speak from facts, as they presented themselves to his eye under the microscope. It was he who had the genius that suggested the examination of the whole process of inflammation, in the living tissues under the microscope. This he accomplished by narcotizing a frog, and while alive, but insensible to pain, a portion of the peritoneum or mesentery, which is almost transparent, so that the circulation may be plainly seen, was fastened with pins upon an ingeniously-devised rack or stage. The inflammation is now excited by etching the membrane with a little acid and a sharp needle, and then the object is placed under the microscope. If the operator is careful, so as not to tear or crush the vessels or tissues, and preserves the moisture, by spraying with warm water from time to time, the circulation and the abnormal processes of inflammation that are going on, may be observed and studied with great exactness for several hours. I will now describe what may be seen in the field of the microscope.