KIDNEYS. 87 



pure hydrochloric acid for twelve hours, and then leave them in water for twenty-four hours. 

 Tease out a small piece in osmic acid solution (one per cent.), and mount it in Farrant's solu- 

 tion. By teasing part of a kidney prepared in this way it has been shown that the Malpighian 

 corpuscle is continuous with a convoluted secreting tubule, which winds about in the cortex, 

 and then descends in a pyramid of Ferrein into the medulla, forming the descending part of 

 the looped tubule of Henle, and reascends as the ascending part of the loop, and after a 

 short course as a connecting tube, with a zigzag direction, becomes continuous with a collecting 

 tube, and descends through a pyramid of Ferrein, and in its course joins at an acute angle 

 with similar tubules, which is thus a discharging tube, opening on the surface of a papilla. 



CONNECTIVE TISSUE OF THE KIDNEY. 



Compare this section with the above. Make transverse sections through the cortex, and also 

 through the medulla near the apex of a Malpighian pyramid, and stain them with logwood or 

 picrocarmine, and mount in Farrant's solution. 



EXAMINATION (L). In the cortex. Observe the convoluted tubules and glomeruli ; 

 notice the small amount of interlobular connective tissue, and search for a transverse section 

 of a group of straight tubules, i.e. of a pyramid of Ferrein. Study the characters of these 

 parts (H). 



(L). Apex of a Malpighian Pyramid. Observe the transverse sections of the discharging 

 tubules lined with clear, low, columnar epithelium, and a well-defined lumen. Notice the 

 large amount of connective tissue between and supporting the tubules, forming a marked 

 contrast to the small amount in the cortex. 



It is desirable to have a transverse section through the boundary line between the cortex 

 and medulla. 



Observe the transverse sections of the collecting tubules, and here and there the cut ends 

 of the ascending and descending looped tubules of Henle ; the narrow loop is not unlike a 

 capillary with its bulging oval nucleus. Sections of capillaries may also be found, but they 

 usually contain blood-corpuscles. Note the moderate amount of intertubular connective 

 tissue intermediate in amount between that of the cortex and medulla. 



Ammonium Chromate Kidney. Heidenhain showed that the epithelial cells lining a 

 uriniferous tubule excepting those of the descending limb of Henle's loop : the loop itself, 

 and all parts of the collecting tube, are made up of a number of ' rods ' or fibrils placed 

 vertically to the long axis of the tube. These rods are most distinct in the outer half of the 

 cells, i.e. next the membrana propria. Each cell contains a spherical nucleus placed about the 

 middle of its substance. 



EXAMINATION (L). Select a convoluted tubule in the cortex, and use (H) to see the 

 above-described characters. They are easily seen in a properly prepared kidney. 



BLOOD-VESSELS OF THE KIDNEY. 



PREPARATION. Make transverse and longitudinal sections of a kidney which has been 

 injected from the renal artery with a gelatine and carmine or Berlin-blue mass. Mount in 

 dammar. 



EXAMINATION (L). Observe large branches of the renal artery running outwards be- 

 tween the Malpighian pyramids ; from these the interlobular arteries proceed vertically 



