Fig. 7. Survey of the papilla of the rat kidney showing mostly cross sectioned collecting tubules (D), 

 thin segments of Henle's loop (T) and capillaries (C). The cells of the collecting tubule are cuboidal with 

 few mitochondria, easilj^ recognized cell boundaries, and tinj- microvilli on the surface. The cells of the 

 thin segment are fairly squamous in sections showing scalloped appearance due to the frequently inter- 

 digitating, narrow cell extensions. The endothelium of the capillaries is extremely thin. In the electron 

 micrograph, there seems to be no chance of mistaking a thin segment for a capillary because of the dif- 

 ference in thickness of the lining cells, but also because of the obvious staining of the blood plasma in 

 the capillaries. The interstitial cell (X) is unidentified. Magnification 2,700X. 



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