1912.] B. cloacae [Jordan] on Citric and Malic Acids. 11 



The effect of the presence of oxygen is to increase the relative proportion 

 of carbon dioxide with respect to the acetic acid. This may be due to the 

 occurrence of reactions such as the following : — 



(2) 4C 6 H 8 7 + 2H 2 + 20, = 8C 2 H 4 2 + 8C0 2 + 2H 2 0. 



(3) 4C 6 H 8 7 + 40 2 = 7C 2 H 4 O 2 +10CO 2 +2H 2 O. 



These give the ratios shown in the following table, which also includes the 

 numbers actually found : — 





Molecular ratio, 



co,_ 



C;H 4 0;' 



Respiratory coefficient, 

 C0 2 

 2 " 





0-67 





2 



10 



4-0 



3 



1-4 



2-5 



Found bv experiment 



0-97 





1-0 







1 -56 







1 -is 









2 35 







3 2 



It is also possible that the decomposition takes place in the same way in 

 the presence or absence of oxygen, according to equation (1), but that in 

 presence of oxygen a portion of the acetic acid is subsequently oxidised. 



Summary. 



(a) Malic acid is not fermented by B. cloacce in the absence of oxygen. 



(b) Malic acid is decomposed by B. cloacce in the presence of oxygen into 

 carbon dioxide, acetic acid, and succinic acid, with traces of alcohol. The 

 decomposition probably goes on in two ways ; oxidation by atmospheric 

 oxygen to carbon dioxide and acetic acid, and oxidation at the expense of 

 another portion of the malic acid, which is thereby reduced to succinic acid. 



"With a good supply of air the respiratory coefficient C0 2 /0 2 and the 

 molecular ratio C0 2 /C 2 H 4 2 found agree well with the values given by 

 a reaction proceeding as follows : — 



3C 4 H 6 5 +50 2 = 2C2H4O2 + 8CO2 + 0H2O. 



(c) In contradistinction to malic acid, citric acid is fermented by B. cloacce 

 in the absence of free oxygen. In addition to carbon dioxide, acetic, and 

 succinic acids, the products resulting from aerobic fermentation, formic acid 

 is produced, while there is an increased production of acetic acid. 



The molecular ratio C02/C 2 H 4 02 found agrees with the value for the 

 following equation : — 



(1) 4C 6 H 8 0; + 4H 2 = 9C2H4O2 + 6CO2. 



