648 DIABETES 



ami, as dest'rilicd under hcxoscs — any sujiar of tliat type will in tlu' ))ioseiire of 

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

 may again split into 3-carl)on 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. 

 Nef formulated the view that — were it not for the occurrence of these irre- 

 versible 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 l)ar to the great equilil)rium is there 

 nonexistent, and it is conceivable that in tlie body there actually exists an c()uili- 

 britun of this sort. 



Ill all of Embden's experiments there was a lack of oxygen, so 

 that the phenomena //( vii'o and in alkaline solution in vitro are strik- 

 ingly parallel. Yet Embden, on the basis of these experiments, re- 

 gards sareolactic acid {i. e. d-lactic) as a chief normal breakdown 

 product of glucose in the body over the glyceric aldehyde route. But 

 it is hard to see why this assumption is any 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 bod}', which 

 it certainly is not. Although lactic acid will disappear from a sur- 

 viving asphyxiated muscle if ox^^gen be resupplied to it (Fletcher) ^^ 

 and although this disappearance will not occur in an alkaline solution 

 experiment, unless some stronger oxidizing agent than ILO2 is used, 

 still it must be remembered that the asphyxiated, lactic acid-contain- 

 ing muscle, has acquired an acid reaction. If the alkaline solution be 

 acidified and a trace of ferrous sulphate added it also permits lactic 

 acid to burn with peroxide, and still we know that the lactic acid was 

 not an intermediate until the oxygen supply became deficient. Lactic 

 acid is probably an intermediate in the sugar catabolism only during 

 relative asphyxia. 



All the substances whose formula? are given above have been shown 

 to be capable of conversion into glucose in the body. The details 

 of the stej)s involved have not been established, but, in conformity 

 with the chemical theories developed by Nef and discussed under 

 liexoses,' the transformation of these substances into glucose, as 

 well as their occurrence in the course of its breakdown, are best ex- 

 ])lained on the basis that all of them participate in the same great 

 chemical equilibrium with the sugars, and that this participation de- 

 ])eiids upon their dissociation into unsaturated residues. These resi- 

 dues* are in dynamic chemical eciuilibrium with the molecules from 

 wiiicli they are derived and with those derived from sugars. When 

 there is a rapid loss of glucose from the body these substances tend to 

 become glucose, in accordance willi llie laws of chemical equilibrium. 



TETROSES 



Tliere are six possible tetroses (4 aldo- and 2 keto-"). The entire 

 subject of their physiology, which has undoubtedly considerable bio- 



17 Jour, of Physiol., 1907 (35), 247. 



