482 



Mr. E. C. Grey. Decomposition of 



be a matter of conjecture, it may with some probability be supposed that 

 it is connected with the presence in the products from mannitol of hydrogen 

 available for reduction. It must be remembered that the two hydrogen 

 atoms possessed by mannitol in excess of those present in glucose are only 

 capable of reducing half the possible amount of B which could be produced 

 from one molecule of mannitol. Hence, even if - half the mannitol were 

 converted into lactic acid, these extra hydrogen atoms could be completely 

 taken up by B. As a matter of fact not more than one-quarter of the 

 mannitol appears as lactic acid, so that a considerable part of B is reduced 

 to alcohol and the remainder probably undergoes the same change as in 

 glucose, forming equimolecular proportions of alcohol and acetic acid. 



It must be noted that from the above considerations one would expect 

 that the production of acetic acid from mannitol by the selected organism 

 would be somewhat less than by the normal. In my figures, however, this 

 is not demonstrated to be the case, but it must be remembered that the 

 amount of acetic acid produced by the selected organism does not exceed that 

 produced from glucose. 



In the absence of more experimental results, however, it would be 

 premature to discuss other possible origins of acetic acid. 



In the scheme for the decomposition of mannitol the production of the 

 excess of alcohol, as compared to the case of glucose, is represented as 

 occurring through the agency of this extra hydrogen. 



In the case of glucose, on the other hand, alcohol can only be produced if 

 there be simultaneously the formation of some oxidation product, or in 

 other words the hydrogen would have to be supplied by a reductase. 



It should be remembered that the aldehydomutase of Cannizzaro which 

 brings about the conversion in this case of two molecules of acetaldehyde 

 into acetic acid and ethyl alcohol is in reality also a reductase, the acceptor 

 for the oxygen being the same as the substance reduced. The essential 

 difference between the two changes would then reside in the necessity 

 for the co-operation of a reductase in the decomposition of glucose which 

 would not be required to the same extent for that of mannitol. 



In all other respects after the preliminary decomposition of the original 

 molecule the two actions would then require exactly the same enzymes. 



Considered dynamically, the reaction by which the intermediate substance A 

 changes into formic acid and substance B occurs more rapidly with mannitol 

 than with glucose, so that in the final products less lactic acid is formed in 

 the case of mannitol than in the case of glucose. 



This acceleration of the reaction in the case of mannitol by which inter- 

 mediate substance A yields ultimately formic acid and alcohol as chief 



