MATTER AND ENERGY 73 



sary, and at the end of the process the amount 

 of enzyme is the same as at the beginning 

 If the enzyme is used up, or if a portion 

 of it is used up, there must be a process 

 by which the enzyme is reconstructed. To 

 avoid this difficulty, it has been supposed that 

 the enzyme acts catalytically, that is, merely 

 by its presence. It is difficult to imagine that 

 any substance can modify a chemical product 

 merely by its presence. This idea arose from 

 the fact that the enzyme appeared to be 

 unaltered in the process. The chemist is also 

 aware of chemical processes influenced by the 

 presence of inorganic substances. Thus a 

 mixture of oxygen and hydrogen immediately 

 explodes when brought into contact with 

 platinum black. If so, we may imagine that 

 some kind of vibratory action is communi- 

 cated to the molecules of the fermentable 

 matter from the enzyme, and that this vibra- 

 tion causes the change in the substance. The 

 analogy is that of sympathetic vibrations 

 between two tuning forks of the same pitch. 

 Thus a fork Ut 4 will, if caused to vibrate 

 by bowing, at once set in action the prongs of 



