THE STRUCTURE OF THE ELEMENTARY TISSUES. 



21 



other dye, such as hematoxylhi, which has the property of picking out 

 its nuclei. 



Endothelial cells may be ciliated, e. g., those in the mesentery of 

 frogs, especially about the breeding season. 



FIG. 15. Part of the omentum of a cat, stained in silver nitrate, X 100. The tissue forms a 

 " fenestrated membrane " that is to say, one which is studded with holes or windows. In the figure 

 these are of various shapes and sizes, leaving trabeculae, the basis of which is fibrous tissue. The 

 trabeculae are of various sizes, and are covered with endothelial cells, the nuclei of which have been 

 made evident by staining with hgematoxylin after the silver nitrate has outlined the cells by stain- 

 ing the intercellular substance. (T. D- Harris.) 



Besides the ordinary endothelial cells above described, there are 

 found on the omentum and parts of the pleura of many animals, little 



FIG. 16. Abdominal surface of centrum tendineum of diaphragm of rabbit, showing the gen- 

 eral polygonal shape of the endothelial cells : each is nucleated. (Klein.) X 300. 



~bud-like processes or nodules , consisting of small polyhedral granular 

 cells, rounded on their free surface, whicli multiply very rapidly by 

 division (Fig. 17). These constitute what is known as "germinating 

 endothelium." The process of germination doubtless goes on in health, 

 and the small cells which are thrown off in succession are carried into 

 the lymphatics, and contribute to the number of the lymph corpuscles. 



