TISSUES. 63 



These cells thus form the inner layer of serous mem- 

 branes, and while structurally they bear a close re- 

 semblance to epithelial cells, there is nevertheless an 

 intrinsic difference made apparent by a comparison 

 of pathological growths from these cells called endo- 

 thelioma, and like growths from epithelial cells called 

 epithelioma. Endothelioma are usually slower of 

 growth, less malignant when malignancy exists, and 

 have a tendency to form mucoid deposits. Endothe- 

 lial cells are mononucleated, 

 scaly, or of the pavement 

 variety with wavy borders, 

 and are held together with a 

 cement substance that re- 

 quires special staining tech- 

 nique to demonstrate. They 

 impart a transparent, smooth, 

 glistening surface to the mem- 

 brane which they clothe. 

 Peritoneum and Pleura. Fig . 29 ._ Ep itheiium or 



These are true serous mem- endothelium from mesentery. 

 - , , r i 1 Silver nitrate stain. 



branes, the structure of which 

 is described on page 60. Elas- 

 tic fibers are particularly abundant in the membrana 

 propria, giving strength to both peritoneum and 

 pleura, so that these membranes are readily sewed 

 in surgical cases. Physiologically these membranes 

 are of the greatest importance : 



i . It is claimed that the simple pavement epithe- 

 lial cells of the peritoneum can produce a secre- 

 tion that clots, and in this manner adhesions are 



