480 



Mr. E. C. Grey. Decomposition of 



Discussion of Results. 



The most significant fact in connection with these results is that whereas 

 in their action on glucose, the artificially selected strains of B. coli 

 communis have been considerably modified, in their action on mannitol the 

 only important change is the non-decomposition in the one case, and only 

 partial decomposition in the other case, of formic acid into carbon dioxide 

 and hydrogen. 



The results with mannitol present greater uniformity than those with 

 glucose, and may be conveniently considered first. It will be seen that the 

 ratio (alcohol + acetic acid)/2 : formic acid* is practically constant and almost 

 equal to unity. Thus 



and points to two conclusions — 



(1) Alcohol and acetic acid are probably derived from an intermediate 

 substance common to them both, and they ma} T therefore, to a certain extent, 

 replace one another. (2) This intermediate substance from which alcohol 

 and acetic acid are produced is itself formed in constant ratio to formic acid. 



Lactic acid might be regarded as being formed directly from mannitol by 

 the action of a special enzyme, but this could only occur if (a) hydrogen 

 were evolved in excess of carbon dioxide, or (b) alcohol and formic acid 

 were produced by the same enzyme which produced lactic acid, as, for 

 example, in accordance with the equation 



But if such a change as is represented by this equation were effected in one 

 step by a single enzyme then, since the proportion of lactic acid actually 

 produced is only one-third of that demanded by this equation (see Table IV), 

 it would follow that there must be another origin for alcohol and formic acid* 



The following hypothetical schemes are put forward to represent the 

 decomposition of mannitol and glucose : — 



C 6 Hi 4 8 = C 3 H 6 03 + C 2 H 5 OH + HCOOH. 



Mannitol, C 6 H 14 6 . 



Lactic acid, C 3 H 6 3 . 



t 



Intermediate substance A + (2H)* 



Formic acid, C0 2 'H 2 . 



Intermediate substance B 



Alcohol, C 2 H 6 0. 



Alcohol, C. 2 H 6 0. Acetic acid, C 2 H 4 2 . 



* Hydrogen is here written as atomic hydrogen to indicate that it is intramolecular. 



* Formic acid includes free carbon dioxide and hydrogen. 



