REN. 



243 



the kidney it frequently happens that the epi- 

 thelial lining of many of the tubes is entirely 

 removed, or only a few particles of epithelium 

 remain scattered over the inner surface of the 

 membrane. " It sometimes happens, that 

 when the epithelium may seem to be alto- 

 gether detached, the basement membrane re- 

 tains, scattered evenly over its surface and at 

 some distance apart, a number of roundish 

 marks, of the size and aspect of the nuclei of 

 epithelium particles. These are most probably 

 the early condition of the new or advancing 

 series of these particles." * The basement 

 membrane is united externally to the capillary 

 venous plexus and the investing fibrous 

 matrix ; there is probably some organic con- 

 nexion between these tissues, which allows of 

 the free transudation of materials from the 

 blood-vessels through the basement membrane 

 to the epithelial cells. When a tube deprived 

 of its epithelium is detached from the sur- 

 rounding tissue, the basement membrane is 

 readily thrown into folds and wrinkles, and 

 appears to possess a considerable amount of 

 elasticity. The thickness of this membrane, 

 according to Mr. Bowman, does not exceed 

 7-o7T.T7T tn f an English inch. In certain 

 diseased states of the kidney its thickness is 

 much increased, and simultaneously the cavity 

 of the tube becomes dilated so as greatly to 

 exceed its normal diameter, thus constituting 

 the serous cysts which are so frequently ob- 

 served in the kidney. 



The basement membrane of the tubes is 

 continuous on the one hand with the capsule 

 of the Malpighian bodies, and on the other 

 through the straight tubes of the pyramids 

 with the basement layer of the mucous 

 membrane which lines the pelvis of the kidney. 



The mean diameter of the tubes is about 

 .j..!.- inch. The entire diameter of the convo- 

 luted tubes in the cortical portion somewhat 

 exceeds that of the straight tubes in the pyra- 

 mids, although the cavity of the latter is 

 greater than that of the former. The latter 

 fact resulting, as will be seen hereafter, from 

 the difference in the character of the epithe- 

 lium in these portions of the tubes. 



After the brief allusion just now made to 

 the epithelium of the tube and its relation to 

 the basement membrane, it will be more con- 

 venient to postpone for the present the par- 

 ticular consideration of this important struc- 

 ture, and to proceed to the examination of the 

 Malpighian bodies. We shall then revert 

 to the epithelium, and we shall find that 

 the varying characters which it presents in 

 different parts of the organ are of the great- 

 est interest and importance in connection 

 with the physiology of the renal secretion, as 

 well as on account of the assistance which 

 they afford in the interpretation of the patho- 

 logical changes to which the kidney is liable. 



Malpighian Sadies. The Malpighian bo- 

 dies have been objects of much interest 

 since their discovery by the distinguished 

 anatomist whose name they bear. Malpighif 



* Art. Mucous MEMBRANE. 



j- Exercitatio Anatom. de Renibus. 



ascertained that these bodies, which he calls 

 internal glands, could be readily injected from 

 the arteries, to the branches of which they 

 are appended. He could not succeed in in- 

 jecting them from the veins, in consequence, 

 as he believed, of valves in these vessels pre- 

 venting the passage of the injected material in 

 a backward direction ; he, however, considers 

 it a rational inference, that the venous radi- 

 cles commence in these bodies. Malpighi 

 further endeavoured to demonstrate the con- 

 nection which he believed to exist between 

 these bodies and the urinary tubes. He made 

 unsuccessful attempts to inject the tubes from 

 the arteries and from the veins : and, finally, 

 he experimented on a living dog, by tying the 

 renal veins and the ureters. On examination 

 of the kidneys after death, there were some 

 appearances of the renal glandules (the Mal- 

 pighian bodies) and the tubes being con- 

 nected and continuous ; but he confesses that 

 his opinion on this point was derived rather 

 from analogy than from ocular demonstration, 

 his idea being that the urinary constituents 

 were separated from the arteries of the Mal- 

 pighian bodies, and that the tubes were the 

 excretory ducts of these glands. 



Ruysch* appears to have been the first to 

 show that the urinary tubes may be injected 

 through the arteries of the Malpighian bodies, 

 and he supposed that the arteries become 

 directly continuous with the urinary tubes. 

 Boerhaave -f- described the cortical portion of 

 the kidney as being composed partly of glan- 

 dular Malpighian bodies, and partly of blood- 

 vessels, which form a plexus without being 

 connected with the Malpighian bodies ; he 

 also inferred the existence of two kinds of 

 excretory ducts, the one kind being connected 

 with the Malpighian bodies, while the others 

 are directly continuous with the blood-vessels ; 

 and he supposed that the more watery portion 

 of the urine is excreted by the latter, while 

 the denser portion prepared in the Malpighian 

 bodies is carried off by the first-mentioned 

 ducts. Berlin J agrees for the most part with 

 Boerhaave as to the anatomy of the kidney, 

 but he assigns to the Malpighian bodies the 

 office of secreting the more liquid portion of 

 the urine, and supposes that the denser parts 

 are separated by those blood-vessels which, as 

 he believed, are not connected with the Malpi- 

 ghian bodies, but are directly continuous with 

 the urinary tubes. 



Schumlansky$, while he confesses the great 

 difficulty of arriving at an accurate knowledge 

 of the structure of the Malpighian bodies and 

 their connexion with the urinary tubes, ap- 

 pears to have had as definite an idea of these 

 parts as it was possible to arrive at with the 

 imperfect means of observation which he pos- 

 sessed. He describes the Malpighian bodies 

 as consisting of a glomerulus of vessels, con- 

 nected on the one side with the arteries, and 



* Thesaurus Anatom. 

 f Institut. Medic. 



J Mem. de 1'AcacL Roy. des Sciences, 1744 Op. 

 cit. 



De StructurS, Renum. Argent. 1788. 



R 2 



