KWXKYS. 217 



Besides this secretory unit, there is a blood vascular unit, which 

 is made up of all those glomeruli and vessels which are con- 

 nected with each interlobular artery and vein (Fig. 165). 



The connective tissue of the kidney is not abundant, but is 

 found in greatest quantity in the papillae. It surrounds the 

 membranse propria? of the urinary tubules and the capsules of 

 Bowman, and carries with it the blood-vessels. The whole 

 kidney is surrounded by the tunica albuginea, a fibrous mem- 

 brane containing smooth muscle. Mall, some years ago, stated 

 that the framework of the kidney is made up of interlacing 

 connective-tissue fibres, which are differentiated at the borders 

 of the tubules to form basement membranes. Such membranes 

 appear in ordinary specimens to be homogeneous, but by 

 methods of digestion (pancreatin) they can be shown to be 

 fibrillar in structure. This has been confirmed by the work 

 of Riihle, Bisse, and v. Ebner. A later publication by Mall 

 shows that the true basement membrane is destroyed by pan- 

 creatin digestion. This leaves only a framework of connective 

 tissue, as stated above. Specimens were obtained by macerat- 

 ing in cold saturated sodium bicarbonate solution, in which not 

 only this framework, but also a membrane closely associated 

 with the epithelial cells was demonstrated. These membranes 

 are neither elastic tissue nor reticulum. Mall suggests that 

 they are possibly identical with the membranes of elastic fibres. 



Blood-vessels of the Kidney. 



The kidney derives its blood supply from the branches of 

 the renal artery. The relations between these and the calyces 

 ami pyramids of the kidney have been described by Brodel. 

 According to him, about three-fourths of the blood which 

 enters the hilum of the kidney by four or five arterial 

 branches, flows through the anterior subdivisions of these 

 branches, while one-fourth is carried through the smaller pos- 

 terior divisions. This is shown in Fig. 171. The anterior 

 branches supply the anterior pyramids and the anterior part 

 of the posterior pyramids ; while the remainder of the organ is 

 supplied through the posterior branches. The blood supply 



