76 PHYSIOLOGY OF BACTERIA 



of energy, as may be seen from the following combustion 

 heats per gram molecule : 



CHa-CHOH-COOH -> CHs'CHsOH + CO2 

 326 cal.* 326 cal.* 



Lactic acid Ethyl alcohol 



COOHCHOHCHOHCOOH -> CH2OHCH2OH + 



287 cal.* 287 cal.*2 p^ 



Tartaric acid Ethylene glycol L/W2 



The uniform distribution of oxygen in the carbohydrates 

 makes them especially fit for intramolecular oxido-reduc- 

 tions. The same holds for glycerol. Hydroxyacids (e.g., 

 lactic, tartaric) and amino acids which by hydrolysis may 

 be changed to hydroxy acids, can also be fermented anae- 

 robically according to type 2. 



The organisms (i.e., the catalysts) which have the faculty to bring 

 about intramolecular changes of this type, can exist anaerobically 

 only if the medium contains compounds of the just-mentioned type. 

 Bad. coli dies without oxygen in a solution containing lactate only, 

 though with access of air, it can utiHze the lactate by using oxygen as a 

 hydrogen acceptor (p. 187). Some peptones contain a compound 

 which permits anaerobic growth of Bad. coli. According to Treece 

 (1928), Bad. coli and aerogenes formed acid and gas in anaerobic 

 solutions of Difco's, and Parke, Davis' peptone, but not with 

 Armour's or Witte's peptone. The products do not seem to be 

 derived from carbohydrate radicals. 



A peculiar exception to the oxido-reductions of organic 

 and inorganic compounds is the urea fermentation which 

 is a hydrolysis. As a rule, the energy yield of hydrolysis 

 is almost negligible (see p. 25). The cause of this 

 exception of urea fermentation is the circumstance 



* Combustion heat. 



