226 INFLAMMATION 



lated or otherwise rendered immobile, so that they block its path, 

 while it is held fixed by the attraction on this side. (c and d 

 explain the formation of solid leucocytic walls about areas of 

 inflammation, and the frequent absence of leucocytes within the 

 central necrotic areas.) (e) The formation of chemotactic sub- 

 stances may cease because the substance causing the inflammation 

 has been used up, or because the bacteria have been destroyed, 

 or from any of the causes that terminate inflammation. Those 

 leucocytes still advancing will reach a point where there is as 

 much chemotactic substance behind as in front they will then 

 stop advancing. As the fluids exuded in the central portion 

 continue to dilute the chemotactic substances and wash them out, 

 there will soon be less chemotactic substance in the center of the 

 inflamed area than there is farther out, hence the leucocytes 

 will move away from the center toward the periphery, following 

 the chemotactic substances back into the blood-vessel and the 

 lymph-stream. These are the conditions that exist at the close 

 of the inflammatory process, which results in the dispersion of 

 the leucocytes. 



General leucocytosis can be explained equally well on the 

 same grounds. Chemotactic substances from the area of inflam- 

 mation enter the blood-stream, and so, in a very dilute form, 

 pass through the bone-marrow. The chemotaxis in the blood 

 will be greater than that of the marrow, and the leucocytes will 

 move toward and into the blood. As long as the blood contains 

 more chemotactic substances than the marrow, leucocytosis will 

 increase, to stop when the amount in blood and marrow is alike 

 or when there is less in the blood than in the marrow. 



Behavior of Tissue-cells and Formation of Giant- 

 cells. The free cells of the tissues involved in inflammation 

 can, of course, obey the same influences as the leucocytes, and 

 apparently do so in so far as they are not checked by structural 

 impediments to flowing motion ; i. e., the more closely a cell is 

 related to a simple drop of fluid protoplasm, the more closely 

 does it resemble in the simplicity of its reactions the " artificial 

 ameba. " Cells with much cytoplasm are best fitted to move 

 freely, as a rule, and hence we see chiefly the large endothelial 

 cells of the lymph sinuses and the serous cavities, and the large 

 hyaline and granular cells of the blood acting as phagocytes, for 

 phagocytosis is no different from ameboid motion which con- 

 tinues about a particle until it is surrounded ; likewise we see 

 the " epithelioid " cells with their abundant cytoplasm fusing to- 

 gether to form giant-cells. (Note that such giant-cells are 

 formed particularly in conditions in which the epithelioid cell is 



