COLUMNAR EPITHELIUM 



57 





obtains more frequently with tissue from the lower animals), and 

 they are always connected by their edges by means of an albumi- 

 nous cement. 



Such a simple squamous epithelium is found in only a few 

 locations. The most important are the alveoli of the lungs, the 



FIG. 31. PAVEMENT EPITHELIUM. DIAGRAMMATIC. 



capsule of the Malpighian body of the kidney, and the descending 

 limb of the loop of Henle in the kidney. Seen from the surface, 

 a stratified or columnar epithelium appears like pavement epithe- 

 lium. 



COLUMNAR EPITHELIUM 



Columnar cells are found, generally, throughout the alimentary 

 and respiratory tracts, except near their external openings. They 

 also line the cerebral ventricles, most of the uriniferous tubules, 

 Fallopian tubes, the uterus, etc. This epithelium is quickly de- 

 stroyed after death, and is difficult of perfect demonstration, 

 except in an animal recently killed. 



Procure from the abattoir a portion of the small intestine and 

 bronchus of a pig, and with the curved scissors snip out small 

 pieces from the mucous surface of each. Macerate in one-sixth per 

 cent, of chromic acid for twenty -four hours. 



Place a piece of the gut on a slide, and, after having added a 

 drop of the acid solution, scrape off the mucous surface with a knife 

 and remove the remainder of the gut. Add a cover -glass, and 

 focus (H). You will find cells in various conditions, from isolated 

 examples to small groups like Fig. 32. 



Observe that the attached ends of the cells are often small and 



