634 



OF SECRETION. 



a. The distinction between the cortical and medullary parts of the Kidney essentially con- 

 sists in this, that the former is by far the most vascular, and the plexus formed by the 

 tubuli uriniferi seems to come into the closest relation with that of the sanguiferous capil- 

 laries, so that it is probably the seat of the greater part of the process of secretion ; whilst 

 the latter is principally composed of tubes, passing in 'a straight line from the former towards 

 their point of entrance into the ureter. In this respect there is a considerable analogy of 

 structure and comparative function, between the two parts of the kidney and the two parts 

 of the brain. The adjoined figure represents the appearances presented by a portion of an 



Fig. 244. 



Portion of the Kidney of a new-born infant; A, natural 

 size; 1, 1, corpora Malpighiana, as dispersed points in the 

 cortical substance ; 2, 2, papilla ; B, a smaller part magni- 

 fied ; 1, 1, corpora Malpighiana ; 2, 2, tubuli uriniferi. 



Portion of one of the tubuli uriniferi, 

 from the kidney of an adult; showing 

 its tesselated epithelium. Magnified 

 250 diameters. 



injected kidney, as seen by the naked eye, and under a low magnifying power. The tubuli 

 uriniferi, in passing outwards from the calices, increase in number by divarication, to a con- 

 siderable extent, as shown in Fig. 246 ; but their diameter remains the same. When they 

 arrive in the cortical substance, their previously straight direction is departed from, and they 

 become much convoluted. The closeness of the texture formed by their interlacement with 

 the blood-vessels, renders it difficult to obtain a clear view of their mode of termination. 

 They seem to inosculate with each other, forming a plexus, with a free extremity, or more 

 probably a loop, here and there (Fig. 24G) ; the number of these free extremities, however, 

 does not appear to be nearly equal to that of the uriniferous tubes themselves. 



b. Scattered through the plexus formed by the blood-vessels and uriniferous tubes, a num- 

 ber 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 examined with a high magnifying power, is found to consist of a mass of minute 

 blood-vessels (Fig. 246, 7) ; somewhat resembling those convoluted masses of Absorbents, 

 termed Lymphatic Glands. Each of these is included in an offshoot from one of the tubuli 

 uriniferi, which swells into a flask-like dilatation to receive it (Fig. 247) ; and every tube 

 may have several such lateral offshoots. The Epithelium which elsewhere lines the tube 

 (whose usual character is shown in Fig. 244) is altered in appearance, where the tube is 

 continuous with this capsular dilatation (Fig. 247, 2') ; being there more transparent, and 

 furnished with cilia (as shown at 2"), which in the Frog may be seen, for many hours after 

 death, in very active motion, directing a current down the tube. Further within the capsule, 

 the Epithelium is excessively delicate; but it may be clearly seen to cover the convoluied 

 knot of vessels, which constitutes the Malpighian body.* The Renal Artery, on entering 

 the Kidney, divides itself into minute twigs, which are the afferent vessels of the Malpighian 

 tufts (Fig. 248, a/). After it has pierced the capsule, the twig dilates; and suddenly divides 

 and subdivides itself into several minute branches, terminating in convoluted capillaries, 

 which are collected in the form of a ball (m. in) ; and from the interior of the ball, the soli- 

 tary efferent vessel, ef, arises, which passes out of the capsule by the side of the single affe- 

 rent vessel. This ball seems to lie loose and bare in the capsule, being attached to it only 

 by its afferent and efferent vessels (Fig. 248, w); but it appears in reality to be enveloped 

 in a reflexion of the membrane that forms the cnpsule; find from this are probably generated 

 the epithelium-cells, by which itis covered. The efferent vessels, on leaving the Malpighian 

 todies, separately enter the plexus of capillaries, p, surrounding the tubuli uriniferi, st, and 

 supply that plexus with blood: from this plexus the Renal vein arises. In Mr. Bowman's 



* On this point, which is one of difference between Mr. Bowman and Dr. Gerlach, the 

 Author's own observations lead him unhesitatingly to concur with the latter. 



