PHYSIOLOGICAL ANATOMY OF THE KIDNEYS. 399 



Malpighian Bodies. Thes3 are ovoid or rounded terminal dilatations of the convo- 

 luted tubes, of somewhat variable size, measuring from ^r^ to T fg- of an inch in diam- 

 eter. They are composed of a membrane continuous with the external membrane of 

 the convoluted tubes, of the same homogeneous character, but somewhat thicker, meas- 

 uring about ^o^o-o f an inch- This sac, called the capsule of Muller, encloses a mass of 

 convoluted blood-vessels and is lined with a layer of nucleated epithelial cells. In 

 addition to the cells lining the capsule, there are other cells which are applied to the 

 blood-vessels. The theory advanced by Bowman in 1842, that the Malpighian bodies are 

 chiefly concerned in the transudation of water, with, perhaps, a small quantity of inor- 

 ganic salts, while the epithelium of the tubes separates the solid excrementitious principles 

 from the blood, has lately been confirmed (1874) by the experiments of Ileidenhain, and 

 is now generally accepted. 



The cells attached to the capsule of Muller are smaller and more transparent than 

 those lining the convoluted tubes. They are ovoid, nucleated, and finely granular. The 

 cells covering the vessels, however, are larger and more opaque, and they resemble the 

 epithelium lining the tubes. They measure from T Vo- to Wo o of an incn m diameter, by 

 about ^yVo- of an inch in thickness. 



Tales of the Cortical Substance. Following out the tubes in the cortical substance 

 from the Malpighian bodies, we find first a short, constricted portion, called the neck 

 of the capsule. The tube soon dilates to the diameter of about -5-^ of an inch, when 

 its course becomes exceedingly intricate and convoluted. These are what are known 

 as the convoluted tubes of the kidney. The membrane of these tubes is transparent 

 and homogeneous, but quite firm and resisting. It measures about ^^^ of an inch in 

 thickness. It is lined throughout with a single layer of rounded epithelial cells, from 

 T _i__ to y-jjVs- of an inch in diameter, somewhat larger, consequently, than the cells lining 

 the straight tubes. These cells are nucleated and usually quite granular. It has heen 

 found that, in many of the lower orders of animals, the cells lining the neck of the 

 capsule are provided with vibratilo cilia ; and it is possible that they may exist in man, 

 although their presence has never been actually demonstrated. 



Kecent researches, particularly those of Heidenhain, have shown that the greatest 

 part if not all of the solid excrementitious constituents of the urine, such as urea and the 

 urates, is separated from the blood by the cells of the convoluted tubes of the cortical 

 substance and perhaps by the dilated portions of the tubes of Henle, while the water of 

 the urine transudes through the blood-vessels in the Malpighian bodies. This view was 

 first advanced by Bowman in 1842. 



Narrow Tubes of Henle. According to the most recent observations, the convoluted 

 tubes above described, after a long and tortuous course in the cortical substance, invari- 

 ably become continuous, near the pyramids, with tubes of much smaller diameter, which 

 form loops, extending to a greater or less depth into the pyramids. The loops formed 

 by these canals (the narrow tubes of Henle) are nearly parallel with the tubes of Bel- 

 lini and are much greater in number near the bases of the pyramids than toward the 

 apices. The diameter of these tubes is very variable, and they present enlargements at 

 irregular intervals in their course. The narrow portions are about s fa ff of an inch in 

 diameter, and the wide portions, about twice this size. The narrow portion is lined by 

 small, clear cells with very prominent nuclei. The wider portions are lined by larger, 

 granular cells. Near the bases of the pyramids, the wide portion sometimes forms the 

 loop ; but, near the apices, the loop is always narrow. The difference in the size of the 

 epithelium is such, that, while the diameter of the tube is variable, its caliber remains 

 nearly uniform. The membrane of these tubes is quite thick, thicker, even, than the 

 membrane of the tubes of Bellini. 



Intermediate Tubes. After the narrow tubes of Henle have returned to the cortical 

 substance, they communicate with a system of flattened, ribbon-shaped canals, measuring 

 from TI Vfr to T ^Vff of an inch in diameter, with excessively thin, fragile walls, lined by 



