318 



EPITHELIAL AND ENDOTHELIAL TISSUE. 



small doses into the blood of a living frog will, after a short 

 time, appear in the cement-substance of columnar and different 

 stratified epithelia, the latter themselves exhibiting no trace of the 

 coloring matter. Excavations in the cement-substance seem to 

 be a necessity for the process of nutrition of the epithelia. In 

 inflammation the cement-substance becomes liquefied, and there- 

 upon admits of a free growth of the filaments and a coalescence 

 of neighboring epithelia into multinuclear bioplasson masses. 

 In the cement-substance of the epithelia of the liver there are 

 regular tubular excavations, the bile-capillaries. 



FIG. 136. DIAGRAM OF THE VARIETIES OF EPITHELIA. 



F, flat epithelia in front view ; 8, same in side view ; Cu, cuboidal epithelia ; Co, columnar 

 epithelia in side view ; T, columnar epithelia in top view ; Ci, ciliated columnar epithelia ; , 

 bacillated columnar epithelia. 



Division. We distinguish mainly three varieties of epithelia 

 the flat, the cuboidal, and the columnar or cylindrical, the differ- 

 ence depending upon the prevailing diameter. (See Fig. 136.) 



Flat epithelia exhibit a broad front surface, while in edge 

 view they are spindle-shaped, because of the gradual narrowing 

 from the middle portion, containing the nucleus, toward the 

 periphery. The cuboidal epithelia derive their name from having 



