ALIMENTARY GLYCOSURIA 517 



sugar, which varies little under normal conditions from 0.1 

 per cent, or one part in a thousand. By converting the sugar 

 brought to it in the portal blood into glycogen, the liver main- 

 tains the proportion of sugar in the blood constant at this 

 small figure. The power of the liver to store up glycogen is 

 not unlimited, however, and hence if too large quantities of 

 sugar are absorbed into the portal vein in a short space of time, 

 not all of it is converted into glycogen in its passage through 

 the liver, and consequently the systemic blood becomes loaded 

 with more than the normal amount of sugar. As soon as this 

 happens the urine begins to contain sugar, for, while the kidney 

 does not excrete more than the most minute traces of sugar 

 from the normal blood, yet any excessive sugar is eliminated at 

 once. The explanation of this will be discussed later. 



Since the storage of sugar as glycogen is performed chiefly 

 by the liver, this fact has been used clinically as a test of the 

 functional capacity of the liver. A normal individual can take 

 from 150 to 200 grams of glucose at one time without glyco- 

 suria resulting ; therefore, if after administration of somewhat 

 smaller quantities, say 100 grams, sugar appears in the urine, 

 we have evidence that the liver is functionally incapacitated. 

 Thus, in cirrhosis of the liver glycosuria often follows the 

 taking of 100 grams or less of glucose. This "assimilation 

 limit" varies under normal conditions for different carbohy- 

 drates. 1 Unlimited quantities of starch may be taken, because 

 its rate of conversion into sugar is slow enough to prevent an 

 overwhelming of the portal blood with glucose. Of the sugars, 

 glucose has the highest assimilation limit (150200 grams); 

 but that of levulose is about as high 2 (140-160 grams), and 

 the sugar eliminated in the urine when levulose is taken is 

 chiefly glucose mixed with some levulose (v. Noorden). Cane- 

 sugar has about the same assimilation limit as glucose, but lac- 

 tose (milk-sugar) has a limit of 120 grams or less. With the 

 two disaccharides just named, any excess that is absorbed 

 unchanged from the intestine into the blood reappears in the 

 urine, for they cannot be utilized by the liver or other tissues ; 

 maltose alone of the disaccharides can be split in the blood, 

 where a specific ferment, maltase, is normally present. Pen- 

 tosescan be assimilated to but a very moderate degree, for when 

 even so little as 30 to 50 grams is taken by mouth, a large 

 amount may reappear in the urine. 



1 See Blumenthal, Hofmeister's Beitr., 1905 (6), 329. 



2 1.9 gm. per kilo in man, according to De Kossi (Kiforma Med., 1904 (20), 



729). 



