THE KIDNEYS. SECRETION OF URINE. 



597 



Fig. 166. 



after its destruction, free nuclei, interspersed among amorphous granules, alone 

 remain in the interior of the tubules. The epithelial cells are arranged more 

 or less regularly on the interior of the basement-membrane, in such a manner 

 that a free channel is left in the centre of each tubule. Scattered through the 

 plexus formed by the bloodvessels and uriniferous tubes, a number of little 

 dark points may be seen with the naked eye, to which the designation of Cor- 

 pora Malpighiana has been given, after the name 

 of their discoverer. Each one of these, when ex- 

 amined with a high magnifying power, is found to 

 consist of a convoluted mass of minute blood- 

 vessels (Fig. 165, 7); and this is included in a 

 flask-like dilatation of one of the tubuli uriniferi 

 (Fig. 166). According to Mr. Bowman, this 

 dilatation proceeds only from the termination of the 

 tubulus ; and this seems to be usually the case, 

 although it seems not improbable that it may some- 

 times be a lateral diverticulum, as described by 

 Gerlach (loc. cit.). The epithelium, which else- 

 where lines the tube, is altered in appearance 

 where the tube is continuous with this capsular 

 dilatation (Fig. 166, &')j being there more trans- 

 parent and furnished with cilia (as shown at b"), 

 which in the Frog may be seen for many hours 

 after death, in very active motion, directing a cur- 

 rent down the tube. Further within the capsule, 

 this epithelium becomes excessively delicate, and 

 sometimes disappears altogether. The surface of 

 the Malpighian tuft is often seen to be studded with 

 nuclear particles, which suggest the idea that it is 

 covered by an epithelial layer } and hence G-erlach, 

 followed by other anatomists, has maintained that 

 the flask-shaped dilatation of the tubulus uriniferus 

 is not perforated by the bloodvessels which form the 

 Malpighian tuft, but is reflected over it. It appears 

 probable, however, that these nuclear particles 

 really belong to the walls of the vessels ; and the 

 most careful examination has failed to detect any 

 such reflexion. On this as on all other points of 

 importance, therefore, Mr. Bowman's original description proves to be unas- 

 sailable. 1 



635. The Circulation of Blood through the Kidney presents a very remark- 

 able peculiarity. The supply is derived in Man (as in other Mammalia) direct 

 from the arterial system ; though in Fishes and Reptiles, the urinary apparatus 

 is connected, as well as the biliary, with the portal venous system, and even 

 in Birds a portion of its blood is derived from the latter. But although this 

 organ is supplied from the renal artery, yet it is not to its proper secretory appa- 

 ratus that the blood of that artery is distributed in the first instance ; for, on enter- 

 ing the kidney, this vessel speedily and entirely divides itself into minute twigs, 

 which are the afferent vessels of the Malpighian tufts (Fig. 167, of). After 

 it has pierced the capsule, each twig dilates ; and suddenly divides and subdi- 



1 The a priori improbability that the basement-membrane of a glandular tubule or follicle 

 should be thus penetrated by bloodvessels, has been entirely removed by the discovery that 

 such penetration does take place in other cases, as the Peyerian glandulse ($ 456) and the 

 Corpora Malpighiana of the Spleen ( 482). 



Uriniferous Tube, Malpighian 

 Tuft, and Capsule, from Kidney of 

 Frog: a, cavity of the tube; 6, 

 epithelium of the tube; 6', ciliated 

 epithelium of the neck of the cap- 

 sule; 6", detached epithelium-scale; 

 c, basement-membrane of tube; c'' 

 basement-membrane of capsule ; m, 

 convoluted capillaries of the Mal- 

 pighian tuft. 



