KIDNEY. 



[ 448 ] 



KIDNEY. 



(fig. 384 b) lined with pavement epithelium, 

 d. The b.asement membrane is very trans- 

 parent, but firm and elastic. Within it is a 

 single laj^er of nucleated polygonal epithelial 

 cells (fig. 384 d, e). These, when immersed 

 in water, lose their polygonal form, become 

 rounded, and appear to fill up the tubules 

 entirely ; they often also burst; and then 

 the tubules appear to contain nothing more 

 than a finely granular mass with nuclei. 

 These changes are found to have taken place 



1. A Malpighian body A, with the urinary tubule B C, 

 human, a, Capsule of the Malpighian body, continuous 

 with 6, the b;i8ement membrane of the tubule ; c, epi- 

 thelium of the Malpighian body : d, that of the tubule ; 

 e, detached epithelial cells; /, afferent vessel; g, effe- 

 rent vessel; k, Malpighian tuft. 2. Three epithelial 

 cells from coiled tubules, one of them containing glo- 

 bules of fat. 



Magnified 300 diameters. 



spontaneously if the kidney is not fresh. 

 But the structure of the tubules varies. 

 Thus, in some parts of the convoluted 

 tubules, the nuclei ajipear imbedded in a 

 pulpy mass or a granular epithelium ; while 

 in others, clear epithelial cells exist, and 

 are larger than in the straight tubules. In 

 the tubuli of the medullary portion, the 

 epithelium is columnar; and in the tubuli of 

 the papillae the basement membrane is 

 ab-ont. 



The Malpighian bodies may be regarded 

 as terminal dilatations of the tubules, ench 

 containing a round plexus of vessels, form- 

 ing the Malpighian tuft. 



The basement membrane surrounding the 

 tuft (fig. 384 a) is somewhat thicker than 

 elsewhere ; and the epithelium lining it is 

 continued over the free surface of the tuft ; but 

 this is denied by Bowman. The Malpighian 

 tufts consist of close convolutions of fine 

 vessels derived from branches of the renal 

 artery. The latter enter the kidney between 

 the pyramids, and continue to divide until 

 arriving at the cortical substance, where 

 they give off" a number of long branches, 

 mostly running towards the convex surface 

 of the kidney, between the lobules, hence 

 called interlobular arteries. From these, 

 short (mostly lateral) branches are given 

 off", each of which terminates in a Malpighian 

 tuft, forming its afferent vessel. Each 

 afferent vessel, on entering the Malpighian 

 body, divides into 5-8 branches, each of 



Fig. 385. 



From a human kidney, a, end of an interlobular 

 artery; 6, aft'erent vessels; e, naked Malpighian tuft; 

 (?, efferent vessels ; e, tufts enclosed in their capsules ; 

 f, ui'inary tubules arising from them. 



Magnified 45 diameters. 



which becomes subdivided into a tuft of 

 capillaries; these are variously convoluted 

 and interwoven, ultimately uniting in a 

 single vessel, the efferent vessel. The afferent 

 and efferent vessels are usually situated near 

 each other, and opposite the origin of the 

 urinary tubule. 



