18 



EPITHELIAL TISSUES 



FIG. 16. SECRETORY CAPILLARIES 

 IN THE HUMAN PANCREAS. 



Z, glandular lumen ; sc, secretory 

 capillaries ; 2, secreting cells. (Af- 

 ter Sobotta.) x 375. 



exoplasm. This cement substance is pierced by numerous minute 

 canals, the secretory or nutrient canaliculi, which are either con- 

 nected with the tissue spaces of the membrana propria, or open 



upon the free surface of the epithe- 

 lium, to which they convey the secre- 

 tion of the cells. The nutrient canals 

 so occasionally are continued directly into 

 the cytoplasm of the cell. 



At the surface of the membrane 

 this cement substance, from exposure 

 to unusual mechanical and chemical 

 influence, becomes altered in consist- 

 ence, and is readily demonstrated by 

 certain staining methods (silver nitrate, 

 hematein, etc.). These condensed por- 

 tions, when viewed from the free sur- 

 face, form a network of " terminal bars," the meshes of which are 

 occupied by the free surfaces of the epithelial cells. 



In the case of many epithelial cells i. e., the polyhedral cells 

 in the deeper layers of stratified epithelium, and many cells of 

 columnar epithelium, the in- 

 tercellular cement substance 

 is . bridged across by numer- 

 ous fine protoplasmic threads, 

 which, arising within the sub- 

 stance of one cell, become lost 

 .in the cytoplasm of its neigh- 

 bors. The peculiar spinous 

 appearance produced by these 

 so-called intercellular bridges 

 has caused such cells to be 

 described as "prickle cells" 

 (Fig. 8). 



The intercellular bridges 

 are more than the name im- 

 plies, for they can often be 

 traced not only from one cell 

 to another, but may even pass entirely through an intermediate 

 cell and enter a third or even a fourth cell. These protoplasmic 

 processes usually follow regular curves with a convexity toward 

 the cell nuclei, so that in passing through a cell they frequently 



FIG. 17. " TERMINAL BARS" OF CEMENT SUB- 

 STANCE AS SEEN BETWEEN THE EPITHELIAL 

 CELLS OF A TUBULAR SECRETING GLAND 

 IN THE PYLORIC REGION OF THE HUMAN 

 STOMACH. 



The columnar epithelium is seen in profile 

 at a ; at 6, the free ends of the cells are seen. 

 Hematein. x 550. 



