FORMATION OF URINE 



219 



THE MECHANISM OF URINE FORMATION 



If the separation of fluid in the kidney is due to filtration, 

 the process must obey the following three laws : — 



1. The amount of filtration will vary directly with the 

 blood-pressure in the glomeruH and inversely with the 

 pressure in the tubules. 



2. The tendency to filtration will be resisted by the 

 osmotic pressure of those constituents of the blood which 

 do not pass through the glomeruh ; filtration ceasing when 

 the filtration pressure is counterbalanced by such osmotic 

 pressure. 



3. Any variation in the amount of urine filtered will not 

 be accompanied by variation in the oxygen consumption of 

 the kidney. 



Let us now see whether these conditions hold. 



1. The Filtration-pressure. — As regards the pressure in 

 the glomeruh the results are set forth in the accompanying 

 table. 



