Discussion 



223 



acid urine in the rat can be produced by the same technique of sodium 

 depletion and intraperitoneal sodium sulphate, which is clearly a more 

 efficient stimulus to maximum acidity. Finally, one would agree that 

 the condition of the kidney has been shown quite clearly to be dependent 

 partly on body potassium stores. Potassium depletion, possibly by 

 decreasing intracellular high-energy phosphate bonds — though that is 

 purely speculation — will decrease the maximum osmolar gradient 

 between urine and plasma, and similarly it will decrease the maximum 

 possible hydrogen ion gradient. This effect is produced by potassium 

 deficiency on the two stimuli of ammonium chloride or sodium sulphate 

 injections. 



McCance : The lower limits might be due to the activitj^ of carbonic 

 anhydrase having a ceiling in the human kidney. We know that if the 

 carbonic anhydrase is defective the lowering of pH is correspondingly 

 limited. 



