224 



URINE 



such as uric acid and potassium, which have a Threshold, 

 but the Threshold, unUke that of the Threshold Bodies 

 proper, is habitually exceeded under normal conditions. 

 All these substances, to whichever category they belong, 

 pass through the glomerulus, but they differ greatly in the 

 degree to which they are reabsorbed. 



No-Threshold Bodies hke urea are not absorbed at all. 

 Threshold Bodies hke dextrose are reabsorbed provided 

 that they do not exceed the threshold in the blood. When 

 the threshold is exceeded, the excess fails to be absorbed 

 and appears in the urine. 



Cushny's example will make this clearer. 



One htre of urine contains 2 per cent, of urea. The blood 



contains '03 per cent. Therefore the Utre of urine is formed 



2 

 from -__ = 67 litres of plasma. The plasma contains 

 •Uo 



62 htres of water. Therefore 62 htres pass through the 



glomerulus. Of this amount 61 htres are reabsorbed. The 



