34 A PRIMER OF BIOLOGY 



and this oxygen is conveyed to the regions of the 

 body that are doing work, and therefore expending 

 energy, there to unite with the elements of complex 

 compounds poor in oxygen and themselves ready to 

 unite with it, and so liberate energy in the kinetic 

 form. It will thus be seen that, to the organism 

 absorbing them, organic compounds form stores of 

 potential energy, by the liberation of which the 

 organism is able to do work, to exhibit vital phenomena 

 in a word, to live, provided always that oxygen 

 gas be available for the oxidation of these compounds. 

 It must not, however, be assumed that these various 

 organic bodies are in all cases oxidised directly and 

 undergo "combustion" in the ordinary sense of the 

 term, like oil in a furnace ; on the contrary, it is 

 highly probable that it is the extremely complex 

 protoplasmic molecule or aggregate of molecules that 

 undergoes decomposition, and that the oxidation and 

 abstriction of simpler decomposition products is in- 

 timately associated with the constructive or assimi- 

 latory phenomena already referred to (p. 27). 



There are other ways of releasing the potential 

 energy of an organic compound, although oxidation 

 may be considered as the chief method. By dis- 

 sociation a complex compound breaks up into two 

 or more smaller and less complex groupings without 

 the entry of any oxygen. There are also decom- 

 positions set up by certain secretions manufactured 

 by the organism itself, but these and other methods 

 need not be considered in the present relation. 



