THE URINARY ORGANS. 



599 



coat, which in its chemical characters is very closely allied to the sarco- 

 lemma (vid. 58), lies a single layer of polygonal, moderately thick 

 cells, surrounding the cavity of the tubulus, which, from the readiness 

 with which they alter, have given rise to many erroneous representations 

 respecting the structure of the urinary ducts and their contents. For 

 instance, in the usual mode of examination in water, they expand, 

 owing to its absorption and become vesicularly distended, so that their 

 polygonal form and regular arrangement are lost ; the renal ducts, 

 within the structureless membrane, appearing to be entirely filled with 



Fig. 246. 



Fis. 247. 



rounded larger cells and no longer to possess any cavity. The cells, 

 also, frequently burst, in which case the tubuli contain nothing but a 

 fine granular substance, with nuclei and clear albuminous drops escaped 

 from the cells. In kidneys not quite fresh, these changes proceed 

 spontaneously ; and, therefore, it is, above all things, necessary to exa- 

 mine the organ as soon as possible after death and to avoid all additions 

 capable of producing change. The contents of the epithelium cells 

 are, besides round nuclei of the usual kind, a most usually, very finely- 

 granular substance, which, on the addition of water, affords clear, light- 

 yellowish drops, probably of albumen, but is not otherwise changed ; 



Fig. 24G. Two straight tubuli uriniferi of Man, one with perfect epithelium, the other 

 half empty : a, membrana propria ; 6, epithelium. 



Fig. 247. 1, a Malpighian corpuscle, A, with the tubulus uriniferus springing from it, 

 J9, C- Human; magnified 300 diam. ; figure half-diagrammatic: a, membrane of the Mal- 

 pighian body, continuous at 6, with the membrana propria of the convoluted tubule ; c, epi- 

 thelium of the Malpighian body; d, that of the tubule; e, detached epithelium ;/, vas afferens ; 

 g, vas effcrens; h, glomcndus Malpighianus. 2, three epithelial cells from the convoluted 

 tubule, magnified 350 diam.; one with oil drops. 



