TRIOSES 0.')5 



first split to ffive two molecules of glyceric aldehyde, as the iunlnlen 

 hypothesis would demand, then glyceric aldehyde would be formed 

 in the body at the rate of O.G gm. per kg. per hour, and tlu; i)lace of 

 formation would be within the cells of the body at large, the muscles 

 representing the most important sites of oxidation. However, if gly- 

 ceric aldehyde is introduced into the systemic blood at only one-fourth 

 of this rate, unchanged triose appears in the urine and may be demon- 

 strated in the blood. But gljxeric aldehyde has never been foimd in 

 the blood, urine or tissues under any other circumstances. Cllyceric 

 aldehyde may of course enter the body via the portal route at faster 

 rates without causing triosuria, but then, as stated, it would appear 

 not to be oxidized directly but first assimilated, i. e., transformed into 

 glucose. Recently, for other reasons, von Fiirth'^ has also questioned 

 the tenability of Embden's h3^pothcsis. 



Lactic acid from triose: When alkali acts on glucose (or hexoses in general) 

 in the absence of oxygen, lactic acid is formed in amounts as high as 40 to 60 

 per cent, of the weight of the sugar used, provided the conditions are properly 

 controlled. But in the presence of sufficient oxygen no lactic acid is formed. 

 Still, preformed, lactic acid will not be destroyed if it is added to this latter mix- 

 ture. So it is clear that lactic acid is not an intermediate in the oxidative break- 

 down of sugars in the alkaline solution. Meisenheimer accordingly suggested 

 the obvious probability that there was some labile precursor of lactic acid which 

 burned in the presence of oxygen; in the absence of oxygen, rearranged to give 

 lactic acid. He proposed glyceric aldehyde as such a body. Nef, however, holds 

 that the immediate precursor of lactic acid is methyl glj-oxal (CH3 — CO — COH), 

 which forms lactic acid by undergoing what is known to chemists as a "benzilic 

 acid rearrangement." These phenomena are remarkably similar to those that 

 occur in the body. 



One other important point should be emphasized in this place. The trioses 

 condense in the presence of alkali to yield among other things certain hexoses, 

 and, as described under hexoses — any sugar of that type will in the presence of 

 alkali enter into a complex equilibrium with several other hexoses. Any of these 

 may again split into 3-carbon compounds such as the trioses and then again con- 

 dense, and so on, as long as they do not become converted into lactic acid or the 

 saccharinic acids — substances which are not reconvertible into sugar. Xef for- 

 mulated the view that — were it not for the occurrence of these irreversible reactions 

 —any sugar in the presence of alkali would come finally to represent an equilibrium 

 of every possible sugar of 2 to 6 carbon atoms {i. e., 56) together with all of the 

 myriad intermediate forms. In the body, however, lactic acid can be converted 

 into sugar. So this bar to the great equilibrium is there nonexistent, and it is 

 conceivable that in the body there actually exists an equilibrium of this sort. 



In all of Embden's experiments there was perhaps a lack of oxygen, 

 so that the phenomena in vivo and in alkaline solution in vitro are strik- 

 ingly parallel. Embden,' on the basis of these experiments, regards 

 sarcolactic acid (i. e. d-lactic) as a c/ize/wormaZ breakdown product of 

 glucose in the body over the glyceric aldehyde route. But it is hard 

 to see why this assumption is more rational than it would be to say that 

 lactic acid is an intermediate in the oxidative breakdown of sugars in 

 the alkaline solution outside the body, which it certainly is not. Al- 

 though lactic acid will disappear from a surviving asphyxiated muscle 

 if oxygen be resupphed to it (Fletcher) 1^" and although this disappear- 



1' Biochem. Zeit., 1916 (69), 199. 

 1^" Jour, of Physiol., 1907 (35), 247. 



