XXVIII.] 



KIDNEY. 



309 



remains distinct, and they are lined by clear nucleated short 

 columnar or cubical epithelium. 



(i.) In the medullary rays in the intermediate layer very narrow 

 tubes the descending portion of the looped tubule of Henle (fig. 

 300), not unlike fine capillaries may be seen, and also the wider, 

 more deeply stained ascending portion of the same tubule. 



2. T.S. of the Apex of a Malpighian Pyramid (Hcematoxylin 

 and Balsam}. 



(a.) (L and H) Observe the large amount of connective tissue 

 between the tubules. The large collecting tubules are cut across, 

 so that their large lumina and the 

 clear columnar epithelial cells lining 

 them are distinctly seen (fig. 298). 

 Not infrequently the epithelium 

 falls out, and then the connective 

 tissue appears as a network with 

 round or oval holes. 



3. T.S. Medullary Ray. Sec- 

 tions should be cut in various direc- 

 tions and at different levels in the 

 cortex. One of the most instructive 

 is to cut a section across the direc- 

 tion of the medullary rays. In it 

 will be seen groups of transverse 

 sections of the various tubes col- 

 lecting, ascending, and descending 

 portions of the looped tubule of 

 Henle which make up a medul- 

 lary ray. Between the rays there 

 are sections of glomeruli and con- 

 voluted tubules. 



Blood- Vessels of the Kidney. The sections should be cut 

 from a kidney injected with carmine gelatine or Berlin-blue gela- 

 tine ; they should be radial, not too thin ; best from the kidney of 

 a small mammal, and mounted in balsam. In injecting a kidney 

 do not use too great pressure, as otherwise the glomerular capillaries 

 are apt to burst, and the injection-mass passes into the tubules. 

 When the stellate veins on the surface are seen to be well injected, 

 one may infer that the mass has traversed the glomerular capillaries. 

 In a small animal inject from the aorta, in a large one from the 

 renal artery. 



4. T.S. Injected Kidney. (a.) (L) Between the cortex and 

 the medulla, i.e., in the boundary or intermediate layer, sections 

 of the larger branches of the renal artery and vein will be seen 

 (fig. 293, KA), i.e., along the "line of vascular supply." From 



FIG. 298. T.S. Apex of a Malpighian 

 Pyramid. A. Large collecting tub- 

 ules; B, C, D. Wide and narrow 

 rts of Henle' a tubule; E, F. 

 -vessels. 



