THE KIDNEYS SECRETION OF URINE. 



493 



arranged in an imbricated manner. In tlie windings of the intermediary 

 portion, the epithelial lining reassumes the pulpy character it presented in 

 the tortuous portion of the tubule. In the main ducts the cells are columnar 

 and well defined, and are attached by their broad bases. In the papillae 

 themselves the ducts lose their basement-membrane, and are composed of 

 the cells alone. 1 On examining one of the Corpora Malpighiana with a high 

 magnifying power, it is found to consist of a convoluted mass of minute 

 bloodvessels (Fig. 180, m); and this is included in a flask-like dilatation of 

 one of the tubuli uriuiferi (Fig. 180, c, c'}. According to Mr. Bowman, 

 this dilatation proceeds only from the termination of the tubulus; and this 

 seems to be usually the case, although it appears not improbable that it may 

 sometimes be a lateral diverticulum, as described by Gerlach (loc. cit.). 

 The epithelium, which elsewhere lines the tube, is altered in appearance 

 where the tube is continuous with the capsular dilatation (Fig. 180, 6') ; 

 being there more transparent, and furnished with cilia (as shown at b"), which, 

 in the Frog and other Reptiles, may be seen for many hours after death, in 

 very active motion, directing a current down the tube (Hiifuer Mecznikow). 

 Beyond this point the wall of the capsule is composed of a mosaic of cells 

 like those forming the walls of the blood- and lymph-capillaries strengthened 

 on the outer side by a little connective-tissue. 



403. The absolute quantity of blood traversing the kidneys is wonderfully 

 great, amounting, according to the calculations of M. Brown-Sequard, 2 to 

 nearly 2000 Ibs. per diem. The Circulation of Blood through the kidney 

 presents a very remarkable 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 apparatus that the 

 blood of the artery is distributed in the first in- 

 stance ; for, on entering the kidney, this vessel 

 speedily and entirely divides itself into minute 

 twigs, which are the afferent vessels of the Malpig- 

 hiaii tufts (Fig. 176,' a, 181, /). After it has 

 pierced the capsule, each twig dilates ; and suddenly 

 divides and subdivides into several minute branches, 

 terminating in convoluted capillaries, which are col- 

 lected in the form of a ball (Figs. 176, b, 181, mm) ; 

 from the interior of the ball, the solitary efferent 

 vessel, ef, arises, which passes out of the capsule by 

 the side of the single afferent vessel. The examina- 

 tions of Kolliker, 3 and of Dr. Isaacs,* show that the 

 glcmerulus is covered with oval nucleated cells. 

 The efferent vessels on leaving the Malpighiau bodies, 

 separately enter the plexus of capillaries (Figs. 176, 

 c, 181, p) surrounding the tubuli uriniferi (st), and 

 supply that plexus with blood; from this plexus the 

 renal vein arises. 5 Thus there is a striking analogy 



FIG. 181. 



Distribution of the Renal 

 vessels; from Kidneys of 

 Horse; a, branch of Renal 

 artery ; af, afferent vessels ; 

 m, m, Malpighian tufts ; ef, ef, 

 efferent vessels ; p, vascular 

 plexus surrounding the tubes; 

 st, straight tube; ct, convo- 

 luted tube. 



1 See Heidenhain, Archiv f. Microscop. Anat., Bd. x; also v. Seng, Sitz. d. k. 

 Akad. zu Wien, 1871, p. 354. 



2 Journ do la Physiol., 1858, t. i, p. 305. 3 Man. Mic. Anat., 1860, p. 408. 



4 Trans of N. Y. Acad. Med., vol. i, 1857. 



5 The reader will find a good summary of the opinions held by Virchow, Ludwig, 

 and others on the course of the vessels, by Dr. Reg. Southey, in the first volume of 

 the St. Bartholomew Hosp. Reports, p. 177. 



