126 THE STORY OF THE LIVING MACHINE. 



carrying on destructive chemical changes, and 

 liberating from the compounds thus broken to 

 pieces their inclosed energy, which is at once con- 

 verted into motion or heat or some other form of 

 active energy. This chemical destruction is, how- 

 ever, possible only after the chemical compounds 

 have become a part of the cell. The cell, there- 

 fore, possesses a nucleus which has the power of 

 enabling it to assimilate its food that is, to con- 

 vert it into its own substance. The nucleus further 

 contains a marvellousmaterial chromatin which 

 in someway exercises a controlling influence in its 

 life and is handed down from one generation to 

 another by continuous descent. Lastly, the cell 

 has the centrosome, which brings about cell divi- 

 sion in such a manner that this chromatin mate- 

 rial is divided equally among the subsequent de- 

 scendants, and thus insures that the daughter cells 

 shall all be equivalent to each other and to the 

 mother cell. 



We must therefore look upon the organic cell 

 as a little engine with admirably adapted parts. 

 Within this engine chemical activity is excited. 

 The fuel supplied to the engine is combined by 

 chemical forces with the oxygen of the air. The 

 vigour of the oxidation is partly dependent upon 

 temperature, just as it is in any other oxidation 

 process, and is of course dependent upon the 

 presence of fuel to be oxidized, and air to furnish 

 the oxygen. Unless the fuel is supplied and the 

 air has free access to it, the machine stops, the 

 cell dies. The energy liberated in this machine 

 is converted into motion or some other form. 

 We do not indeed understand the construction of 

 the machine well enough to explain the exact 

 mechanism by which this conversion takes place, 



