76 BACTERIAL METABOLISM 
This is essentially the equation for many bacteria which ferment 
glucose with the production of lactic acid and H2 and CO2. It should 
be remembered that these equations were primarily worked out for 
yeast fermentations. Harden^ has found that B. coli causes a very 
similar series of changes. The principal difference between the 
Harden and the Neuberg equation, aside from the part played by 
acetaldehyde, seems to be that B. coli produces formic acid first, and 
then through the action of the enzyme, formiase, the formic acid is 
decomposed into H2 and COo according to the equation H.COOH — ^ 
CO2 + H2. Frankland and Frew- had previously shown that formic 
acid accumulates in anaerobic cultures of B. coli; it is practically 
absent in aerobic cultures. 
The completed equation, so Harden states, occurs in three stages. 
1. C6Hi206 = 2CH3.CHOH.COOH. 
2. CeH.sOs + H2O = C2H6OH + CH3.COOH + 2H.C00H. 
3. 2H.C00H = 2H2 + 2CO2. 
The complete reaction, therefore, becomes: 
2C6H12O6 + H2O = 2CH3.CHOH.COOH + CH3.COOH + C2H5OH + 2H2 + 2CO2. 
This equation in its completed form is identical with the Xeuberg 
equation. The occurrence of formic acid has been a subject of much 
controversy. There is no doubt that at least a great majority of 
bacteria that produce CO2 and H2 from glucose also decompose for- 
mates with the formation of CO 2 and H2.^ On the other hand, it is 
not at all certain that yeasts do produce formic acid. Herein may be 
the slight difference between Neuberg's and Harden's results, which 
otherwise are remarkably coincident although attained by quite 
different methods. 
Butyric Fermentation.— Pasteur, studying certain anaerobic "vibrios" 
nearly seventy years ago, noticed that these organisms possessed the 
rather remarkable property of producing butyric acid from the fer- 
mentation of lactates. This predicates the ultimate formation of a 
fatty acid containing four carbon atoms from a hydroxy-acid contain- 
ing three carbon atoms. Neuberg and Arinstein^ have found that cer- 
tain butyric acid-producing bacteria, as Bacillus butylicus fitzianus, 
through Neuberg's "Abfangverfahren," produce both butyric acid 
and butyl alcohol: acetaldehyde was also produced at the same time. 
The exact steps are as yet not worked out. 
Acetic Fermentation.— Liebig^ showed long ago that the acetic acid 
fermentation was not merely an oxidization of ethyl alcohol, and that it 
' Jour. Chem. Soc, 1901, 79, 610; Jour. Hyg., 1905, 5, 488. 
2 Jour. Chem. Soc, 1892, 61, 254. 
•' Pakes and JoUyman: Jour. Chem. Soc, 1901, 79, 386, 459. Franzen and Greve: 
Ztschr. f. physiol. Chem., 1910, 64, 16, 261. 
* Biochem. Ztschr., 1921, 117, 269. 
^ Quoted by Hofmann: Faraday Lecture for 1875, MacMillan & Co., 1876, p. 112. 
