58 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



In the foregoing paragraphs are given some of the more 

 important atomic groupings which are met with in the sub- 

 stances which form the subject matter of bacteriological and 

 enzyme chemistry ; the point must be emphasised that where- 

 ever they occur, and however complicated the atomic groupings 

 may be with which they may be associated, they can always 

 be recognised by their specific reactions. 



A short table summarising the reactions of the few t3rpical 

 groupings which have been considered may therefore be found 

 useful (Table I). The unsaturated linkings, it must be 

 understood, may combine with groups of atoms of greater 

 or less complexity symbolised by R. 



Constitutional Formulae.— In determining the constitution 

 of a compound the main problem consists in ascertaining 

 by the reactions given what atomic groupings are present. 

 To take a simple case, a substance is found by the methods 

 already indicated to have the molecular formula CH4O. Upon 

 oxidation it is found to yield an aldehyde and finally an acid. 

 We conclude, therefore, that it contains the group CHjOH, 

 and bearing in mind that the carbon atom is uniformly 

 tetravalent, we assign the constitution CH3OII and write the 

 equation expressing its oxidation as follows : — 



HCHoOH + = HCHO + H^O 

 HCHO+0=HCOOH 



The substance is, of course, methyl alcohol yielding on 

 oxidation formaldehyde and formic acid. 



Isomerism. — A little reflection will already have suggested 

 that it is possible, even though the number of atoms in a 

 molecule may be identical, that the arrangement of atoms 

 within the molecule may differ in different cases. In con- 

 sidering the constitutional formula for benzene, the assump- 

 tion of a ring arrangement of the carbon atoms in the molecule 



