INTRODUCTORY DISCUSSION. 17 



display such a variety of metabolic products and reactions. As a possible 

 explanation of this great instability and variability of reaction of the 

 sugars, the theories and results of some of the recent chemical investigations 

 give the most helpful suggestions yet offered. It has already been shown 

 that sugars behave like very weak acids, that the hydrogen atoms of the 

 hydroxyl groups can be replaced by metals to form salts. A. P. Mathews 1 

 has shown that the salts formed with sugars are easily ionized and thus lead 

 to increased concentration of sugar anions. These, by virtue of partially 

 unbalanced charges, are very unstable and highly reactive. The most 

 reactive part of the sugar molecule is probably the first carbon atom, the 

 carbonyl group ; thereafter the reactivity decreases down the chain of carbon 

 atoms, as these are removed from the carbonyl group. While the sugars 

 are relatively stable substances, their salts decompose very readily. 



The manner in which these salts decompose is of greatest importance to 

 an understanding of glycolysis. In this decomposition or dissociation the 

 sugar molecule is broken in fragments composed of carbon atoms in varying 

 number. Thus a hexose may break into fragments containing 5 and 1 

 carbon atoms, into fragments of 2 and 4, and into 2 pieces each containing 

 3 carbon atoms. The proportion in which any of these pieces are formed 

 depends upon a number of factors, such as concentration of the sugar, 

 temperature, etc. This dissociation or cleavage of the sugars results in 

 mixtures of tremendous complexity. Of special importance is the fact that 

 these pieces are unstable and of high reactivity, so that they react in a 

 variety of ways; either the pieces undergo intramolecular rearrangements 

 to form more stable compounds, or they may react with each other, oxidizing 

 one and reducing the other ; they may condense or polymerize, or finally 

 unite with other substances present, such as oxygen, to form acids. It can 

 readily be seen what an appalling complex of substances and tangle of 

 reactions are involved in a system containing, for instance, dextrose and 

 sodium hydroxide. Nef has found that in such a system there are finally 

 in equilibrium no less than 93 different substances. Including the syntheses 

 which always accompany these reactions, the number of products is con- 

 siderably above 100. 



It is undoubtedly due to the ease and multifarious ways in which the 

 sugars are dissociated and undergo chemical changes involving the libera- 

 tion of energy that they can be used by the organism both under aerobic 

 and anaerobic conditions. In this respect neither the fats nor the proteins 

 can be compared with the sugars as to the possibilities of usefulness for the 

 organism. It is impossible to give here the detailed chemical steps used in 

 these considerations ; reference must be made to the very extensive original 

 literature. The arguments are based upon the following principles which 

 are applicable alike to hexose, pentose, or tetrose sugars : There are formed 



1 MATHEWS, A. P. The spontaneous oxidation of sugars. Jour. Biol. Chem., 6, 3, 



1909. 



