166 PHYSIOLOGY OF BACTERIA 



dioxide besides oxygen for growth, and that the bacteria 

 first reduced CO2 to HCHO which could be found to 

 exist as such in the culture. 



Urea does not seem to be suitable as a source of carbon. 

 At least, Sohngen (1909) could not cultivate urea 

 bacteria on urea alone, while very small amounts of 

 organic acids (10-20 mg. of ammonium malate or 

 asparagin in 50 c.c. solution) sufficed to bring about 

 normal development of Bad. erythrogenes and of Uroh. 

 jackschii. 



Methane can be used only by the Methanomonas 

 (Sohngen, 1906) and it is not certain that the methane as 

 such is the building stone to be hewn. It might well be 

 that these bacteria use CO2 as the starting point for 

 shaping the parts of molecules for growth as do all other 

 prototrophic bacteria. This carbon dioxide might origi- 

 nate from methane oxidized completely by the same cells. 



The organisms which can use compounds with only one 

 carbon atom must possess the ability to couple carbon 

 atoms. It is interesting to notice that while the coupling 

 of single carbon atoms is possible to all chlorophyl 

 plants, but only to a very limited number of chlorophyl- 

 free organisms, a large number of the latter are able to 

 grow on compounds with two carbons, e.g., alcohol or 

 acetic acid. Many molds can do this; also vinegar 

 bacteria, some yeaSts, Oidium, all Mycodermae and many 

 bacteria can live on acetates. It appears to be much 

 easier to couple two carbons with two carbons than to 

 couple one carbon with another. How this coupling is 

 actually done we do not know with certainty, but it 

 seems possible that we have processes similar to the 

 formation of aldol from aldehyde: 



CHs-CHO + CH3CHO = CH3CH(OH)CH2CHO 



