=Coagulation Necrosis.=--Coagulation necrosis is the term applied to the characteristic changes occurring in the tissue cells when thus attacked, which may be summarized as a fading away of cell outlines, diminution in reaction to reagents, and a merging of cells and intercellular substance. Coagulation necrosis is not the only result of bacterial activity, but may be produced by other causes. Nevertheless, pyogenic bacteria do not exert their deleterious action upon the tissues without occasioning changes included under this term. In an area thus infected, as already described, leukocytes, _i. e._, phagocytes, are present in increased number for purposes already mentioned. As we approach the centre of activity phagocytes are more numerous than cells, and intercellular barriers completely break down. When bacteria are found in greatest number, there also occurs the greatest phagocytic activity, and there also will be found the evidence of suppuration, _i. e._, _pus_. As already indicated, the _polynuclear leukocytes_ are most active in the process of defence. Where coagulation necrosis is most marked there has been the greatest activity of conflict with the greatest death of cells. Around these areas bacteria and cells are found in indiscriminate arrangement. Tissue vitality is impaired by intoxication of the cells by the excretory products of the bacteria, _i. e._, the so-called ptomains, toxins, etc., and their power of resistance is thus weakened. From the mechanical results of pressure tension around the centre of activity is increased, by which tension vitality is still more impaired and more rapid tissue death occurs. Thus there occurs migration or burrowing of pus; or, to state it more clearly, the tissues break down in front of the advancing destruction, and in the direction of least resistance. This is known as the _pointing of pus_, which brings it many times to the surface, and often in other and less desirable directions.