THE ORGANS OF EXCRETION 



meruli) and are gathered by a complicated arrangement 

 into larger divisions, and finally empty into the enlarged 

 upper portion of the ureter. From the little bunches of 

 capillaries spreads throughout 

 the cortex a fine network of 

 capillary tubes, which gather 

 into veins and pour the blood 

 into the renal vein. 



380. Nervous Supply of the 

 Kidneys. The kidneys receive 

 nerves from the renal plexus 

 upon each side. This is com- 

 posed of both white and gray 

 nerve fibers and of nerve cells. 

 They come from many sources, 

 but mainly from the sympa- 

 thetic system by way of the Fi e 12 - -Diagram of a longi- 



. J ~/ J . , tudinal section of a kidney, 



solar plexus. The renal plexus 



a renal artery. 



c capillaries. 



g glomerulus. 



t uriniferous tubule. 



v renal vein. 



has thus indirect connection 

 with the vagus and with other 

 nerves distributed to the inter- 

 nal organs. These nerves seem to have only vasomotor 

 functions. As yet, we are unable to trace the special 

 secretory nerves of the kidneys. 



381. Functions of the Kidneys. The food which we eat, 

 after rendering to the tissues of the body its proper serv- 

 ice, is converted into the waste products water, carbon 

 dioxide, small quantities of salts, and urea (or some sub- 

 stance closely allied). The first two excretions result 

 from decomposition of the carbohydrates and fats, while 

 from the proteids come certain salts and nitrogen. These 

 last are excreted almost wholly by the kidneys, along 

 with a large quantity of water and a very little carbon 



