24 



Physiology of the Kidney 



XYLOSE 



INULIN-SORBITOL- 



MANNITOL 



HYPERGLYCEMIA 



INULIN 



CREATININE 



GLUCOSE 

 SUCROSE 



XYLOSE- 



SORBITOL 



MANNITOL 



UREA 



PHLORIZINIZED 



FIGURE 4 



Figure 4. Diagrammatic summary of the present evidence, based on clearance ratios, 

 indicating that the inulin clearance is at the level of glomerular filtration in man. 



series of studies with these hexahydric alcohols we find that 

 their concentration ratios, and therefore their renal clear- 

 ances, in both dog and man are identical with the inulin 

 clearance with a standard deviation of about 4 per cent. 

 These observations are summarized in Figure 4. Though 

 sorbitol and mannitol are similar to glucose in that they con- 

 tain a number of hydroxyl groups, the absence of either a 

 free aldehyde or ketone group, as in the sugars, argues tenta- 

 tively against their being actively reabsorbed by the mechan- 

 ism that reabsorbes glucose, and the identity of the three 

 clearances is, I believe, good evidence that all three substances 

 are excreted by filtration without tubular reabsorption. 



To bring all the evidence together I would briefly note a 

 few additional facts. Shannon has recently shown that in the 

 dog^^ and man (unpublished) during hyperglycemia, when 



