DEVELOPMENT AND FUNCTION OF MACROPHAGES IN BONE-REPAIR. 31 



heightened phagocytic power, as revealed by their increased dye-content. It may 

 be inferred, therefore, that this waste material, the result of the trauma, is con- 

 cerned in some way with the mobilization of the phagocytes and with their accel- 

 erated activities; that, in fact, the increase in macrophagic tissue, in volume and 

 in functional efficiency, is a response to the presence of dead or dying tissue. 



From table 2 it is also plain that as the dead tissue vanishes, as shown by the 

 tinctorial and histological evidence, the macrophages become less and less con- 

 spicuous, their numbers being reduced and their staining weaker. This points to 

 some connection of the phagocytes with the absorption of the debris. More will be 

 said upon this point later. 



Another evidence that tissue resorption has been proceeding coincidently 

 with the presence of macrophagic tissue in excess is the thinning and rounding of 

 the ends of the bones surrounded by the phagocytes. This, for instance, is seen at 

 the sixth day (S 11-2) in the cleared rib. 



As table 2 shows, some of the phagocytes are found in numbers somewhat 

 above normal after demonstrable debris has disappeared. These are to be looked 

 upon as cells which have persisted in the field after their work was done. They 

 undergo gradual diminution in number and in reaction to the vital dye and are 

 probably to be looked upon as resting rather than as actively functioning. 



To anyone familiar with the literature it will be quite obvious that the behavior 

 of these phagocytes, in the reaction following bone injuries, is quite like that which 

 obtains in the repair of any damaged tissue, and thus the problems involved are 

 those common to inflammation. These problems have been investigated by various 

 writers, as Maximow (1902, 1906, 1909 2 ) and Goldmann (1912); the latter studied 

 the tissues of the vitally stained animal following the application of turpentine and 

 infection with the tubercle bacillus. Tschaschin '(1913), too, investigated the reac- 

 tion of the vitally stained cells in the neighborhood of foreign bodies in the loose 

 connective tissue and in cauterized areas of the liver, spleen, and mesenteric lymph- 

 nodes. Thorough discussions of the various aspects of macrophage behavior under 

 these conditions are to be found in the literature, so that it is here sufficient to refer 

 only to some of the more outstanding points and to emphasize the special application 

 of macrophage function to the repair of bone-wounds. 



We have seen that in the rise and fall of excess macrophagic tissue in the areas 

 surrounding bone-wounds a curve is traced. From this three successive segments 

 may be taken to block out periods of macrophage history in which the most out- 

 standing features of the phagocytic tissue are consecutively development, actiri///, 

 and decline; but it must be recognized that these periods grade insensibly into one 

 another, so that if arbitrary limits be assigned to them there will be of necessity 

 some overlapping. They serve, however, to separate the discussion into convenient 

 subdivisions. 



DEVELOPMENT. 



Of special interest in connection with the development of the macrophage- 

 tissue is the question of origin of these phagocytes of the soft parts. Among the 

 possible sources there must be considered the macrophages found normally in the 



