THE KIDNEY. 131 



large size and the connection, which can often be traced, with the 

 interlobular artery.) 



2. Convoluted tubules. (The convoluted tubes found just be- 

 neath the capsule of the kidney generally belong to the distal 

 variety ; and they are not as favorable specimens as the deeper 

 proximal portions, on account of the crowding of the tubular ele- 

 ments in the outer cortical regions. Select a transverse section and 

 observe :) 



(a) The thin membrana propria, or wall of the the tube. (It 

 does not appear to be made up of fibrillated connective tissue ; but, 

 rather, presents a homogeneous structure. Nuclei, however, may 

 occasionally be seen, which apparently belong to this tissue.) 



(b) The peculiar lining cells. (They are unlike any other paren- 

 chymatous elements found in the body. Note that, while they are 

 evidently of the columnar or cylindrical type, they differ greatly in 

 form and size. The protoplasm is hazy, granular, and frequently 

 striated. They take a dirty brick-red hue from the eosin.) 



(c) The lumen. (Compared with the diameter of the tube-wall, 

 the lumen is very small, and presents a stellate figure. The urine, 

 in passing through the tubule, is, consequently, brought in contact 

 with a very considerable portion of the parenchymatous lining.) 



3. The large proportion of the cortical area occupied by 

 the convoluted tubules, and the exceedingly small amount of 

 intertubular connective tissue. 



4. The intertubular capillaries. (These are exceedingly small, 

 and difficult of demonstration unless they be filled with blood. The 

 nuclei of the endothelial wall are frequently seen. The cells of the 

 convoluted tubules are not infrequently detached from the membrana 

 propria, and the space so formed may be mistaken by the careless 

 observer for longitudinal sections of capillaries. These vessels are 

 much better seen in an injected kidney; although if an organ be 

 selected containing considerable blood, and the corpuscular elements 

 have their color preserved (as in bichromate hardening), the vessels 

 will be easily demonstrated. 



5. Ascending limb of Henle's loops, in the cortical labyrinths. 

 (The general course of these tubules is confined to the pyramids of 

 Malpighii and Ferrein; but occasionally one of them may be seen 

 passing in a tortuous course toward the outer cortex, running be- - 

 tween the proximal convoluted elements. They are easily recognized 

 by their small size and relatively large lumen. They are lined with 

 short columnar or cuboid cells, which stain deeply blue with the haema.) 



6. The pyramids of Ferrein. 



