THE EPITHELIAL TISSUES. 



57 



thelial lining of which may be taken as a type of this variety of 

 tissue. 



The functional activities of epithelium are in marked contrast to 

 the comparatively inert character of endothelium. The cytoplasmic 



FIG. 40. 



Transitional epithelium from bladder of the mouse. (Dogiel.) 1, 2, 3, and U indicate the layers 

 of cells, not everywhere equally well defined, a, hyaloplasmic surface, and, 6, cyto- 

 plasmic body of large superficial cell ; c, leucocyte i. e., white blood-corpuscle that has 

 wandered into the epithelium by virtue of its amoeboid movements ; d, karyokinetic 

 figure in a cell belonging to the deepest layer. Beneath this layer is the fibrous tissue, 

 which is covered by the epithelium and forms a part of the wall of the bladder. The 

 superficial cell, which is fully represented, contains two nuclei, a not very infrequent 

 occurrence in these cells. 



nature of the epithelial cell, when contrasted with the poverty in 

 cytoplasm of the cell in endothelium, would lead us to expect this 

 difference in the cellular activities of the two tissues. At the begin- 

 ning of this chapter a sketch of the manifold functions of epithe- 



FIG. 41. 



Transitional epithelium. Isolated cells from the bladder of the frog. (List.) 



Hum was given. It is a fair general statement of its usefulness to 

 say that epithelium is chiefly concerned in bringing about chemical 

 changes in substances brought to it. Sometimes these substances 

 are elaborated into fresh cell-constituents, and the activity of the 



