BACTERIA AS CHEMICAL AGENTS 



4. Hydrolysis: the addition of HgO to the molecule, a step 

 which is usually followed by a splitting of the molecule at 

 the link hydrolysed. 



5. Deamination: the removal of -NH2 from the molecule. 



6. Decarhoxylation : the removal of COg from -COOH. 



7. Phosphorylation : the esterification of the molecule with 

 phosphoric acid — usually accomplished by the transfer of 

 the phosphate radicle from some substance other than 

 phosphoric acid itself. 



8. Dephosphorylatio7i : the removal by hydrolysis of phos- 

 phoric acid from phosphorylated compounds. 



These eight possibilities may all be utilised in the attack on 

 a given molecule by different bacteria. It is the fact that 

 different bacteria can and do utilise different methods of 

 attack on the same substrate molecule that gives rise to the 

 varied products of bacterial activity and to the apparently 

 involved and complicated metabolism of the order as a whole. 

 The metabolism of the cells of highly organised tissues 

 living in a constant environment, such as those of the mam- 

 malian body, seems to be simple compared with that of 

 bacteria which live in varied environments. The blood of the 

 rat does not differ greatly from the blood of man and the 

 metabolism of a rat muscle-cell, rat liver-cell, or rat kidney- 

 cell does not differ greatly from the metabolism of human 

 muscle-, liver-, or kidney-cell, or from the metabolism of 

 similar cells in another rat. But the metabolism of a 

 cell in a culture of Escherichia coli may differ greatly from 

 that of a cell of the related Aerohacter aerogenes or even 

 from that of a cell of another culture of Escherichia coli 

 grown under different conditions. The metabolism of the 

 bacterial cell is dependent not only on the intrinsic or 

 potential composition of the organism but also on the 

 environmental conditions holding during its division from the 

 mother-cell. To take an example, consider the molecule 

 of pyruvic acid, CH3.CO.COOH. The muscle-cells of 



