46 DESCRIPTION OF FIGURES. 



PLATE 4 Continued. 



FIG. 15. The groups a, b, c, and d (see plates) were drawn with the aid of the camera lucida from typical large pha- 

 gocytic roticulum cells selected from the callus spaces of the tenth, twelfth, fifteenth and twentieth 

 days respectively. The sections were cleared without counterstaining and the dye-granule contour 

 only is represented. In the interior of the cell the nucleus is indicated by the clear space. Only mature 

 phagocytes were selected in each stage. They resemble one another closely and show a certain amount 

 of increase in size with age of callus. In each case, the drawings were made from cells situated in areas 

 where active osseous resorption was going on. X 1,000. 



FIG. 16. A space in callus, showing developing macrophages of the reticulum (M). Camera-lucida drawing from 

 peripheral region of callus at the twelfth day of repair in long bone. Some of the cells are clear, while 

 others contain varying amounts of dye-stuff. The granules are at first small, but gradually increase 

 in size and number. Large intercellular spaces will be noticed. Blood vessels are not shown in this 

 figure, but in the older spaces at this stage they were large and abundant. X 1,000. 



FIG. 17. Drawing made from a tracing from a photomicrograph of the twentieth-day stage of repair. Section cleared 

 without counterstaining. In the lower left corner the old bone and marrow cavity is seen. Around 

 it the callus is arranged, and in many of its spaces there are crowds of black granules, representing 

 macrophages of the reticulum. X 50. 



Fin. 18. A small field from the callus of figure 17, much enlarged. Drawing traced from a photomicrograph. Throngs 

 of maerophages (A/), heavily loaded with dye-granules, present themselves between the osseous tra- 

 beculae (C). These cells are seen more highly magnified in figure 15rf. X 190. 



