134: PRACTICAL MICROSCOPY. 



form the papillary ducts, the lining cells will be seen to get shorter, 

 and the lumina larger.) 



(b) Spiral tubes. (These can be, in many instances, followed 

 down from the pyramids of Ferrein; and examples are frequently seen 

 very near the pelvis of the kidney in the cortical columns.) 



(c) Descending limbs of Henle's loop. (These tubes are the 

 most difficult of all the tubuli uriniferi to demonstrate. The sec- 

 tion must be very thin, and, even then, they may be mistaken for 

 blood capillaries. Their peculiar feature consists in the wavy lumen, 

 which is produced by the alternate disposition of the lining cells.) 



(d) Loop of Henle. (The loops will be recognized by the curv- 

 ing of the tube. They are lined with short columnar cells which are 

 sharply brought out by the haema. On account of their course, but 

 few complete sections are seen. ) 



(e) Ascending limbs. (Conveniently traced from the loop.) 

 (/) Intertubular blood-vessels. (Do not mistake tubules con- 

 taining blood, for capillaries. The human kidney is rarely absolutely 

 normal; and blood is frequently found outside the proper channels. 

 The vessels will be differentiated by the histology of their walls. 

 Quite a number of venules will be seen running in groups in the 

 medulla the venulce rectce.} 



8. The same elements as in 7. (shown in a transverse section of 

 the middle of a Malpighian pyramid, Fig. 91). 



