50 



NORMAL HISTOLOGY. 



are approximately of the same diameter in all directions. They 

 may be almost strictly cubical or spherical, but are usually polyhed- 

 ral as the result of mutual compression, their contiguous surfaces 

 being flattened. They are usually disposed in a single layer upon 

 a surface furnished by the underlying tissues, as, for example, in 

 tubular or racemose glands, but they may be aggregated to form a 

 solid mass of cells filling a sac, as in the sebaceous glands of the 

 skin, or in strands or columns, variously disposed, as in the liver 

 and suprarenal bodies. 



It is this form of epithelium that is chiefly concerned in perform- 

 ing the functions of secretion, and, for this reason, it is frequently 

 designated as " glandular epithelium." 



The appearance of the individual cells varies considerably accord- 

 ing to the functions that they perform and the stage of functional 

 activity which obtained at the time cellular changes were arrested 

 Avhen the particular specimen was prepared for study. It will suf- 

 fice for present purposes of description to call attention to the fact 

 that the cytoplasm is usually highly granular, partly because of its 

 own structure, partly because many of the substances elabo- 

 rated and stored within the cells as the result of their functions 

 appear in the form of granules (metaplasm). The nature of these 

 granules varies. They may be albuminoid, zymogenic granules, or 

 minute drops of fatty substances, which may coalesce to form dis- 

 tinct oily globules, or they may consist of carbohydrates, e. g., gly- 

 .cogen. The granular condition of the cytoplasm may be so marked 



FIG. 27. 





FIG. 28. 



IBlP 



Cubical epithelium. 



FIG. 29. 



Fig. 27. Six cells from the sublingual gland of a man who was executed. (Schiefferdecker.) 

 Fig. 28. Three isolated cells from the gastric tubules of the dog and cat. (Trinkler.) 

 Fig. 29. Cell with highly granular cytoplasm, the result of stored metaplasm, chiefly gly- 

 cogen. (Barfurth.) 



as to render the detection of the nucleus difficult in unstained speci- 

 mens (Figs. 27, 28, and 29). 



In this form of epithelium the presence of two nuclei in a single 

 cell is more frequent than in the other varieties. 



