All observers agree that in actively inflamed tissues the number of cells is very greatly increased. A certain increase may be accounted for by that which has already been described--namely, the escape into the tissues of the wandering cells from the bloodvessels. But neither this alone nor the products of their rapid proliferation are sufficient to account for all the cells found in the truly inflammatory condition. It is now well established that in connective tissue there are two varieties of cells--the fixed and the wandering--the former concealed in the trabeculæ of the intercellular substance, while the latter are small, ordinarily round in shape, much resembling the white corpuscles, possessed of ameboid characteristics, and having the power of changing position. These are known as the wandering cells, which meander through the lymph spaces of the tissues or back and forth into and out of the blood-vascular system, their migration being regulated by causes not yet known. Under natural conditions their number is relatively small. Once given a true inflammatory disturbance they are reproduced with amazing rapidity; and their numbers, added to those produced by diapedesis of leukocytes, with the combined proliferative activity of both forms, serve to account for the new cells whose presence characterizes phlegmonous and other similar disturbances. That these wandering connective-tissue cells have much to do with these changes is shown by the unmistakable evidences of excessive activity known as _karyokinesis_ (_i. e._, _nuclear activity_). Karyokinesis is common not only in inflammatory disturbances, but in new-growths of rapid formation, especially sarcomas, which are formed from mesoblastic cells, the same which have to do with connective tissue. Endothelial cells also undergo the same changes.