METABOLISM OF CARBO-HYDRATES 



543 



they normally follow. Glycuronic acid has been previously men- 

 tioned as a substance occurring even in normal urine in small 

 amount. It is very closely related to dextrose, as a comparison of 

 their constitutional formulae shows: 



COOH 

 H C OH 



OH C H 



I 

 H C OH 



OH 



i 2 OH 



d-dextrose. 



CH a OH 



rf-glyconic acid. 



COOH 



rf-glycuronic acid. 



Glycuronic acid agrees with dextrose in containing the character- 



istic aldehyde group CTT, but differs in that by oxidation two 



atoms of hydrogen in the primary alcohol group CH 2 OH have been 

 replaced by one atom of oxygen. There is reason to believe that 

 in the tissues glycuronic acid can be formed from dextrose in the 

 same way, possibly through the mediation of an enzyme, and it 

 may therefore represent a stage in the katabolism of sugar. But 

 it is not known whether this is a normal transformation through 

 which the whole or the greater part of the dextrose passes, or only 

 a transformation involving a small part of the sugar under normal 

 conditions. The appearance in the urine of large quantities of 

 glycuronic acid, paired as already explained with , various com- 

 pounds, in certain pathological states or after the administration 

 of certain drugs (p. 482) , might be explained either as the result of 

 an increased production of that substance through a deflection of the 

 normal trend of carbo-hydrate degradation, or as the result of a failure 

 on the part of the cells to further transform the glycuronic acid in 

 the quantities normally produced. 



Lactic acid is the one intermediate stage in the decomposition of 

 dextrose in the tissues whose importance seems to be definitely 

 ascertained. The muscles and the liver have been proved to possess 

 the power of producing lactic acid from dextrose obtained directly 

 from the blood or from the hydrolysis of their own store of glycogen, 

 and there is little doubt that this power is shared by many, perhaps 

 by all, of the other organs. There is also good evidence that the 

 lactic acid thus formed can be, and under normal conditions is, in 

 large part oxidized so as eventually to yield carbon dioxide and 

 water, although there is reason to believe that a portion of it may 

 be utilized for the synthesis of more complex bodies. 



The chemistry of the change or series of changes by which lactic 

 add is produced from dextrose and the end-products, carbon dioxide 



