GROWTH 167 



We must consider in the further discussion that the 

 number of carbon atoms in most of the compounds of the 

 cell is an even one. We find most dominantly six 

 carbons (carbohydrates, leucin, benzene ring) but four 

 carbons are not uncommon in bacterial metabolism 

 (butyric, succinic and hydroxy-succinic acids) and the 

 fats, as is well known, contain only the acids with even 

 numbers of carbon atoms. The most common excep- 

 tions to the dominance of even numbers of carbons in 

 cell compounds are lactic acid and glycerol. 



The compounds with three carbons are very commonly 

 used, perhaps because they give, when coupled, the 

 carbon skeleton of the sugars. Lactic acid is sufficient 

 for the entire carbon and energy supply of Mycoderma, 

 Oidium and probably of many other molds and bacteria 

 like Bact. coli. 



The assimilation of higher alcohols and higher organic 

 acids is shown in two tables by Buchanan and Fulmer 

 (II p. 431 and 438) after data from de Jong (1926). 



Even with sugars, we have not in all cases the proof that they 

 are sufficient as a source of carbon, for in most experiments, an 

 organic source of nitrogen is offered, which may supply carbon as well 

 as nitrogen. In order to be really certain that sugar is sufficient for 

 the carbon supply, we must give the nitrogen either in mineral form, 

 or as an amino-derivative of sugar, or eventually as amino-derivative 

 of the decomposition products of sugar (e.g., amino acetic acid in 

 the case of Bact. coli, or of vinegar bacteria) . That yeasts can grow 

 with ammonia nitrogen from sugar alone has already been shown by 

 Pasteur. Most molds behave in the same way. The difficulty in 

 settling the question of carbon supply really rests with the nitrogen 

 source. If an organism cannot use ammonia, nitrate or urea, but 

 requires an organic source of nitrogen, we can tell but little about the 

 carbon supply. 



The customary conception of carbon requirements for 

 growth as presented above has become quite questionable 



