362 THE METABOLISM OF THE CARBOHYDRATES 



dextrose and phloretin, the dextrose being passed into the urine 

 and the phloretin back into the blood, where it combined with 

 the blood sugar to re-form phloridzin, which again underwent 

 decomposition in the renal cells. Meanwhile, some of the phloridzin 

 would leak into the urine, so that renewed doses would have to 

 be given to keep up the diabetic state. 



That the action of phloridzin is located in the kidney has been 

 pretty conclusively shown by Zuntz. This worker found that 

 when phloridzin is injected into the renal artery of one kidney, 

 the urine excreted by that kidney becomes saccharine before the 

 urine from the opposite kidney. 



Minkowski's theory supposes that it is the blood sugar which 

 escapes into the urine. If, however, a surviving kidney be per- 

 fused through its blood-vessels with defibrinated blood containing 

 phloridzin, the urine meanwhile excreted will be found to contain 

 much more sugar than can be accounted for by what has disap- 

 peared from the blood (Pavy, Brodie, and Siau 27 ). The sugar 

 in the blood is derived from the gastro-intestinal tract and liver ; 

 when, therefore, the abdominal viscera, excepting the kidneys, are 

 removed from the circulation the percentage of sugar in the 

 blood falls. The dog can be kept alive 1 for several hours after 

 this operation. If now, into such an eviscerated dog, phlorizdin 

 be injected intravenously, sugar will be found to appear in con- 

 siderable amount in the urine, but the percentage of sugar in the 

 blood will fall no lower than if no phloridzin had been given. In 

 the light of these observations it is impossible that the blood sugar 

 can be the source of the urinary sugar. It is much more 

 reasonable to suppose, as Pavy, Brodie, and Siau have done, that 

 the sugar is formed in the kidney itself out of some precursors 

 contained in the blood. In this respect, the kidney comes to 

 act like the mammary gland ; its cells form sugar out of the non- 

 saccharine constituents of the blood. Phloridzin would seem to 

 confer secretory powers on the renal cells, in other words, to make 

 the kidney in part glandular in function. 



The importance of this recently offered explanation of the 

 action of phloridzin makes it desirable that some of the evidence 

 on which it is based be briefly given here. 



1. Diuretics like cafTein, nitrate of soda, &c., cause an increase 

 in the amount of sugar contained in the urine in those forms of 



1 In a state of unconsciousness. 



