PRODUCTS OF METABOLISM 165 



The last two groups of organisms, alcoholic and lactic, represent 

 complex fermentations. There are several products formed, and as has 

 already been pointed out in the paragraph on the equation of fermen- 

 tations, the entire fermentation cannot be described accurately by one 

 equation, for different fermentations operate independently and simul- 

 taneously in the same cell. Under slightly different experimental 

 conditions the one or other of these simultaneous fermentations may be 

 favored, accordingly a varying proportion of the products are formed. 



The typical representative of the acid-gas forming group of micro- 

 organisms which cause acid-gas fermentation are B. coli, and its near 

 relative. Bad. aerogenes. Many of the gas-formers in nature belong in 

 this group; the bacteria of the fermentations of pickles, sauerkraut, 

 salt-rising bread, the gassy fermentation of milk are some of the many 

 representatives. They are distinct rods, with good surface growth, 

 and do not liquefy gelatin. They are commonly spoken of as the coli- 

 aerogenes group. Some of them have peritrichiate flagella, while 

 others are not motile. 



The fermentation of dextrose brought about by these organisms 

 has been described originally by Harden in the equation: 



2CGH12O6 -t- H2O =, 2C3H6O3 + CH3CO2H + C2H6OH + 2CO2 -I- 2H, 



Dextrose Lactic acid Acetic acid Alcohol 



Harden himself stated later that this equation holds only for one 

 strain, and that we have several different strains distinguished by a 

 proportion of products quite different from the one suggested by the 

 equation. Recently Kamm has shown that a good mineral food 

 (probably phosphates are the essential agent) favors a formation of 

 gas and of volatile acids, while a scant supply of minerals causes the 

 bacteria to produce mainly lactic acid. We must assume, therefore, 

 at least two simultaneous independent fermentations: 



CeHiaOe = 2C3H6O3 



and 



CeHiaOe + H2O = CH3CO2H + CH3CH2OH + 2CO2 -|- 2H2 



The first equation is already known to us; it is the true lactic fermenta- 

 tion. The second equation may be divided still further into several 

 simpler equations. 



B. typhosus, causing typhoid fever, is closely related to B. coli, but 



