486 KIDNEY. [CHAP. XXXTV. 



even here it lias only a faintly granular appearance, and we have 

 been unable to see any distinct fibres. 



It appears to us that this structure is of little physiological im- 

 portance ; it probably serves as a support for the tubes and capillary 

 vessels. 



As the tortuous tubes in the cortex pass in and out amongst the 

 interspaces of this matrix, portions appear to be circumscribed, as 

 it were, giving the idea upon a section of a number of small cysts,* 

 an appearance which is often very marked in certain cases of 

 disease, when the tubes are enlarged. In the kidneys of many 

 rodents, especially in that of the mouse, this appearance exists in a 

 very marked degree, in consequence of the highly developed con- 

 dition of the matrix in these animals; but, in all the instances 

 alluded to, the true structure of this part, and often the continuity 

 of the tube as it winds in and out, can be demonstrated with ease. 

 A thin section of the cortical part of the kidney, made in any 

 direction, displays these interspaces containing sections of the 

 tubes, between which may often be seen vessels which have been 

 cut across. 



Uriniferous Tubes. The uriniferous tubes, formerly termed tubes 

 of Bellini, in which the characteristic elements of the urine are se- 

 creted, consist of two distinct portions, as already alluded to ; the 

 first, or highly convoluted part of the tubes, which is probably the 

 sole seat of true secretion, and the straight portion, which is directly 

 continuous with the former, and conducts the secretion towards the 

 opening upon the mamilla, from which it passes into the pelvis of 

 the kidney. In the other direction, the convoluted portion of the 

 tube terminates in a dilated extremity, which completely invests 

 the vessels of the Malpighian tuft.f 



We shall now consider, first, the minute structure of the 

 Malpighian bodies ; secondly, that of the convoluted portion of the 

 tube ; and, lastly, that of the straight portion. 



Malpighian Bodies. The Malpighian bodies are met with in all 

 vertebrata. In the mammalian kidney, where there exists a di- 

 vision into cortical and medullary portions, they are only found 

 in the former. In an injected specimen, they appear, to the un- 

 aided eye, as coloured points abundantly scattered throughout 

 the cortex of the organ. They vary much in size in different 



* On Diseases of the Kidneys, by George Johnson, M.D. 

 t Phil. Trans., 1842. 



