30(5 HlACTlCAL HISTOLOGY. [XXVIII. 



lial cells are somewhat cubical, but their outlines are not well 

 denned. They each contain a spherical nucleus, and their proto- 

 plasm is "rodded," especially at the outer part. In the spiral 

 tubule the cells are not unlike those of the convoluted tubule, but 

 they are not so tall, and therefore leave a more distinct lumen, and 

 they are not so markedly "rodded." In the descending part of the 

 loop and the loop itself very narrow (10-15 /x,) the cells are 

 clear and flattened, with a bulging opposite the nucleus, and 

 these projections alternate with those on the opposite side of 

 the tubule. The ascending limb (30 p wide) has somewhat 

 cubical cells, which leave a regular lumen. They are striated, 

 and often present an imbricate arrangement. The irregular or 

 zigzag tubule bends on itself with sharp angles, and is wide, 

 with an irregular lumen. Its cells stain deeply with staining 

 reagents, and are conspicuously striated in their outer part. The 

 second or distal convoluted tubule is like the proximal. The junc- 

 tional and collecting tubules are lined by low, columnar, clear, trans- 

 parent cells with small nuclei. The cells do nob stain readily. 

 In the discharging tubules the cells have the same general character, 

 but they are taller and more columnar. Fig. 294 shows the general 

 arrangement of the tubules, and from it it is easy to see in what 

 part of the kidney each kind of tubule is placed. 



Blood- Vessels. The renal artery enters the kidney, splits into 

 branches which run towards the cortex, and at the junction of the 

 cortex and medulla form incomplete arterial arches (fig. 293). 

 From these arches arise the radiate or interlobular arteries, run- 

 ning in the cortex between two medullary rays in a radial direction 

 towards the surface. They give off at intervals on all sides short, 

 slightly-curved vessels vasa afferentia which run without branch- 

 ing to end within the Malpighian capsules, and there form the 

 glomeruli. The vas efferens comes out of the Malpighian capsule 

 close to where the afferent vessel enters it and at the pole opposite 

 to the origin of the uriniferous tubule. The efferent vessel splits 

 up into capillaries, which ramify amongst the tubules of the cortex. 

 The blood is returned from the cortex by interlobular veins (fig. 

 293), which run alongside of the corresponding arteries. The 

 medulla is supplied by leashes of vessels vasa recta which for 

 the most part proceed from the arterial arches. The vasa recta are 

 pencils of arterioles (10-15), splitting up into capillaries which 

 ramify between the tubules of the medulla ; the medulla, however, 

 is not so vascular as the cortex. The blood is returned by corre- 

 sponding veins. The connective tissue is very scanty in the cortex, 

 but abundant in and near the apices of the Malpighian pyramids. 



Methods. (i.) Harden small pieces in a 2 per cent, solution of 

 potassic bichromate (1820 days) or Miiller's fluid. Corrosive 



