CHAPTER XXL 



THE KIDNEYS. 

 BY C. LUDWIG. 



ON dividing the fresh kidney of a Mammal from the papillae 

 to the fibrous capsule, we may discern even with the naked 

 eye a distinction in the exposed surface between the striated 

 medullary portion and the granular cortex. These two seg- 

 ments are concentrically arranged. If the blood and urinary 

 vessels of the organ be injected with differently coloured fluids, 

 they may be observed to pursue a radial direction, both in the 

 medulla and in the cortex. 



On the exposed surface of the medulla, striae radiate from 

 the papillae towards the cortex, which are coloured by the fluid 

 injected into the urinary tubules. 



These striae are in immediate contact at and a little above 

 the papillae, so that up to this point the medulla presents a 

 uniform tint, and the term papillary region has been applied 

 to it. As the strise recede from the papillae, they separate 

 from each other, so that previously to their entrance into 

 the cortical layer they run with intervals of about their own 

 diameter. The intervening spaces are occupied by vessels 

 presenting the colour of the fluid that has been injected into 

 the bloodvessels. That portion of the medulla in which the 

 urinary and blood vessels alternate with one another is termed 

 the limiting or marginal layer of the medulla. In the cortex 

 striae also occur, which, both from the kind and intensity of 

 their colour, as well as from their direction, evidently constitute 

 the immediate prolongations of those striae of the medulla 



G 2 



