82 V. E. EMMEL 



its nucleus are observed to have assumed a more rounded form 

 and not infrequently a more basophilic stain reaction. Instances 

 of such changes involving only single cells or small groups of 

 cells are especially evident in the visceral epicardium. Cells 

 may be observed in which the nuclei instead of being oval or 

 flattened are more rounded or spherical in shape and not in- 

 frequently indented in a kidney shaped manner (figs. 17 and 42). 

 The cytoplasm also is rounded up, the cell as a whole projects 

 from the mesothelial surface and in some instances is attached 

 by only a slender basal cytoplasmic process (fig. 41). It may be 

 observed that as a rule the cytoplasm of such cells also presents 

 a more basophihc stain. Many of these cells have every ap- 

 pearance of being destined to become subsequently detached 

 from the coelomic wall, and it appears evident that when liber- 

 ated into the body cavity they would be practically indistin- 

 guishable in either nuclear or cytoplasmic structure from the 

 macrophags already present in the serous fluid. The important 

 point that the mesothelial cell may function in a phagocytic 

 manner seems clearly demonstrated in figure 42 showing eryth- 

 rocytic inclusions in the mesothelial cytoplasm. Figure 44 

 represents a section through a region of the visceral epicardium 

 in which the prohferative activities involve a larger number of 

 cells. Many of the apparently recently liberated cells are pha- 

 gocytically active, present vacuoles and bud-like cytoplasmic 

 processes and appear identical with the typical coelomic 

 macrophags. 



Are we to conclude from such data that the coelomic meso- 

 thelium is really giving rise to coelomic macrophags? In view 

 of the close approximation of many of the mesothelial cells to 

 the macrophags in both their cytological characteristics and 

 potential phagocytic functions, as observed with the present 

 technique, it would not appear a great step to their differentia- 

 tion into such cells. But a substantial proof of such a process 

 is a more difficult matter especially from fixed material where 

 all the intermediate stages in a given case cannot of course be 

 directly observed. In evaluating the present data it seems 

 clear, however, that the form and surface relations of the cells 



