518 



MANUAL OF HISTOLOGY. 



we have seen, undivided for long distances towards the "bases of the 

 pyramids, possess a lining of gland cells only 0*0158 mm. high. 



The gland cell of the looped canals is, on the other 

 hand, in the descending arms and curves, a very 

 flat pavement element, presenting great similarity 

 to the endotheliurn of the vascular system ( 87). 

 Its nucleus also, as in the latter, projects slightly 



#i jjjjf beyond the surface (fig. 511, d). The resemblance 

 m Jm| / ^0 these vascular cells is really very striking. 

 m JH The recurrent tubes, however, oiHenle's loops com- 

 mence sooner or later to enlarge, and from this on the 

 lining cells assume a different character. Instead 

 of clear, flattened elements, the ordinary cubical gland- 

 cells with distinct nuclei and granular protoplasm pre- 

 sent themselves, with not unfrequently ill-defined 

 boundaries between each one and its neighbour. 

 Hence the recurrent arm becomes cloudy or granular 

 in appearance, and its lumen decreases in diameter. 



These points are very well seen in fig. 511, which 

 is taken from the kidney of the infant. Here may 

 be recognised, at a, the transverse sections of the 

 open canals ; at b, the clear, flat, epithelial cells of 

 the descending tubes ; and at c, the granular clouded 

 gland elements of the recurrent arm of the looped 

 uriniferous canals. 



We must, of course, expect to find the number 

 of sections of tubes filled with dark gland-cells, increasing more and 

 more as the cortex is approached. 



The clearest insight into the ar- 

 rangement of parts, just described, is 

 to be obtained from preparations in 

 which the open canals have been 

 injected from the ureter with one 

 colour, and the blood-vessels of the 

 medulla with another. 



Above, at the termination of the 

 medullary substance and commence- 

 ment of the cortex, the distinctive 

 differences between the two species of 

 tubes disappear more and more, as far 

 as diameter and epithelial lining are 

 concerned. But even here injection 

 from the ureter exhibits the peculiari- 

 ties of the two systems ; for, though 

 the open canals are easily filled, the 

 urine-secreting looped tubes remain, as a rule (unless special modes of 

 treatment be adopted), completely devoid of the fluid injected. The 

 upper portion of the medullary substance assumes, on injection of the 

 blood-vessels, a deep red hue for a considerable depth. This is the 

 boundary layer of Henle. Its deeper colour is due to the presence of 

 numerous tufts of radiating vessels. 



Fig. 510. Looped canals 

 from the renal pyramid 

 of an infant, o, 6, the 

 two arms; c, another 

 tube ; c/, capillary blood- 

 vessel. 



Fig. 511. Transverse section through a renal 

 pyramid of an infant, a, collecting tube with 

 columnar epithelium; 6, descending arm of 

 a looped canal with flat cells; c, recurrent 

 arm with granular epithelial elements; d, 

 transverse section of a blood-vessel; e, fibrous 

 sustentacular tissue. 



