238 BACTERIOLOGY. 



vidual atoms are more firmly bound to one 

 another in the very simple molecules that 

 serve as a starting-point than they are in the 

 complicated synthetic products. Carbonic acid 

 and water, out of which starch and sugar are 

 formed by green plants, are simple molecules, 

 and the atoms in the molecule are firmly 

 united as compared with the more complicated 

 and more unstable molecules of starch and 

 sugar formed out of the same atoms. Car- 

 bonic acid, water, sulphuretted hydrogen, am- 

 monia, and nitric acid, all of which may enter 

 into the synthesis of proteid are very simple, 

 stable atomic compounds compared with the 

 loose and complicated combinations in which 

 these same atoms are bound in the proteid 

 molecules. Along with an increase in the 

 number of atoms in the molecule not only the 

 number of atom-groupings increases, but gen- 

 erally also the looseness of combination. Con- 

 versely also, if a complicated and unstable 

 molecule be broken down, and fall to pieces 

 into simpler and more stable compounds, the 

 ease with which the breaking-down is accom- 

 plished and the number of possible new com- 

 binations must be in general dependent upon 

 the complexity of the demolished molecule. 

 In a molecule built up out of simple com- 

 pounds there exists just as much energy or 



