The Excretion of Sugars by the Kidney. 211 



in the blood. During its passage through the cell some of it is 

 oxidized and if not too much has gotten in all will be oxidized 

 and none appear in the urine. 



In testing out this hypothesis we have referred to published 

 figures for the concentration of various substances in the blood 

 and urine and have also made some experiments of our own. 

 We have found that very roughly speaking a dog of 10 k. body 

 weight with a blood sugar content of .1 per cent, should excrete 

 about .7 g. sugar per hour if the kidney were completely permeable 

 and secreting freely. During marked diuresis Barcroft and 

 Brodie 1 found that about 660 c.c. of oxygen would be required 

 by the dog's kidneys for the same period. 0.7 g. of sugar requires 

 520 c.c. of oxygen for complete oxidation to C0 2 and water. The 

 correspondence is fairly close. 



We have also used published figures for the blood flow through 

 the kidneys and have estimated that the sugar content of the 

 renal vein should be about 80-90 per cent, of the sugar content of 

 the renal artery if the kidney is completely permeable. We ob- 

 tained simultaneous samples of the blood from the femoral artery 

 and renal vein and found in five experiments a difference of 10-15 

 per cent., in three experiments no difference and in two a slightly 

 higher content in the renal vein than in the artery. We drew 10 c.c. 

 samples and analyzed the oxalated plasma by Shaffer's method. 

 In only one of our experiments was any glucose found in the 

 urine and then only a trace. We are engaged at present in trying 

 to improve the analytical methods and will not go into further 

 details. 



We have tested a number of sugars and the indications are at 

 present that only the sugars that are oxidized by the body will show 

 this so-called threshold phenomenon. We believe we are justified 

 in making the following statement: If the kidney is permeable 

 for a sugar when and only when its concentration in the blood 

 rises beyond a certain level, that sugar is oxidized by the kidney. 1 



1 Barcroft and Brodie, Journal Physiol., 33, 52 (1905-06). 



'We even venture to suggest on purely theoretical, grounds the following: If 

 the kidney is permeable for any substance when and only when its concentration in 

 the blood rises beyond a certain level, that substance is metabolized by the kidney. 



