Glucose and Mannitol by B. coli communis. 483 



products, may be due to the reduction of substance B to alcohol whereby it 

 is removed from the sphere of the decomposition of A. 



If, then, the reductase were to be diminished as the result of selection on 

 chloroacetate agar, the removal of B from the sphere of decomposition of A 

 would be slower. The decomposition of A into more of B and formic acid 

 would therefore be specifically hindered, and as a result the production of 

 lactic acid relatively increased. 



This is what is actually observed. On the other hand the decomposition 

 of mannitol would be unaffected, as is also found to be the case. 



The view that the artificially selected strain produced by growth on 

 chloroacetate agar is deficient in some reducing mechanism is further 

 supported by the fact that many of these strains show diminished power of 

 growing anaerobically. Moreover it might be expected that this method of 

 selection would lead to the survival of a strain deficient in reductase, for 

 a strain with a highly developed reducing mechanism would probably convert 

 monochloracetic acid to acetic acid with the liberation of hydrochloric acid, 

 which would certainly not be of advantage to the organism. Such a process 

 might therefore lead to the survival of the strain in which the reducing 

 mechanism was poorly developed. 



Summary and Conclusions. 



Two artificially selected strains of B. coli communis obtained by growth of 

 normal B. coli communis (Escherich) on agar containing sodium chloro- 

 acetate have been examined quantitatively as regards their action on glucose 

 and mannitol. In both cases the selected strains produced from glucose, 

 lactic acid in relatively greater, and alcohol, acetic and formic acid in 

 relatively less, proportion than did the original strains from which they 

 were derived, whereas from mannitol there was no diminution in the 

 production of alcohol, acetic, and formic acid. 



From these results it is inferred that the artificially selected strains have 

 not lost the enzymes which bring about the final reaction in the production 

 of alcohol and acetic acid, but that the process of artificial selection has led 

 to an absence or diminution of the reducing mechanism of the cell so that 

 some intermediate substance, from which formic acid and the precursor of 

 alcohol and acetic acid are derived, cannot be readily decomposed. 



In conclusion I wish to express my thanks to Prof. Harden, F.R.S., in 

 whose laboratory this work has been done. 



