THE URINARY APPARATUS 



pelvis of the kidney, whence it passes into the ureter, and so on to the 

 bladder. The cells by which the urine is secreted vary in form in different 

 parts. Those lining the little bulb or capsule of Malpighi are flattened; 

 those in both of the convoluted portions are columnar and striated or 

 fibrillated; whilst those lining 

 the loop of Henle are flattened 

 and clear in the descending, 

 and striated in the ascending 

 portion. These differences in 

 the character of the cells seem 

 to be associated with differ- 

 ences in function, for, if certain 

 colouring-matters are injected 

 into the blood, they are not 

 found in the cells lining the 

 capsule, but they deeply stain 

 those parts in which the 

 striated cells are found. 



The arrangement of the 

 blood-vessels of the kidney 

 presents several points of great 

 interest. In the first place 

 they are very large for the size 

 of the organ, and consequently 

 the whole mass of the blood 

 circulating the body traverses 

 the kidneys in a comparatively 

 short space of time. Now the 

 constituents of the urine, being 

 of a poisonous nature, are 

 jealously removed from the 

 blood by the cells of the kid- 

 ney as soon as they enter it. 

 In consequence of this rapid 



excretion we find that under healthy conditions very delicate chemical 

 examination is requisite to demonstrate their presence in the blood at all. 



Thus, for example, the quantity of urea discoverable in the blood passing 

 to the kidney by the renal arteries does not exceed 0*016 part in 1000 in 

 health, and is still less in the venous blood returning from them. 



In the next place, there is a double system of capillary vessels which is 

 not found in any other organ of the body. The renal arteries entering 



ferous Tubules 



a, a. Artery; v, s, vein; c, Malpighian corpuscle, a. The eori 

 or cortical substance. B, Boundary layer, c, Papillary portii 

 showing the loop of Henle. 



the 



