THE VITAL PHENOMENA OF BACTERIA. 105 



constitutional formula can be written either 

 H.COOH or, to express its relations to the 

 aldehyde group, HO.COH. 



Compounds that contain both the aldehyde 

 group COH and the carboxyl group COOH 

 are aldehyde acids. We can therefore write 

 two molecules of formic acid simply 2H.COOH 

 or 2HO.COH, or we may also, in accordance 

 with the reaction in which it takes part, conceive 

 it as an aldehyde acid, HO.COH H.COOH. 

 Within an organism, different sorts of reactions 

 may well take place side by side while the 

 chemist is able to determine their occurrence 

 only separately in separate test-tubes. The 

 following reactions may in this case occur 

 directly : 



I. HO.COH H.COOH = COH.COOH + H 2 O 

 formic acid, formic acid, glyoxylic acid. 



II. COH.COOH = CHOH + CO 2 

 glyoxylic acid, formaldehyde. 



Glyoxylic acid, the simplest of the aldehyde 

 acids, may be an intermediate stage between 

 formic acid and formaldehyde. Konigs has 

 already pointed out that in the green plants, 

 glyoxylic acid arises through condensation of 

 two molecules of formic acid. Formaldehyde 

 might be obtained also, as stated above to bo 

 the case with oxalic acid, by reduction of formic 

 acid : 



