80 THE NATURE OF LIFE 



and if the cell lies in a salt solution the 

 flow of the current will be in proportion 

 to the permeability of the cell to these 

 particles. In the normal condition only 

 a few particles can penetrate and little 

 current passes, but as it dies, the salt en- 

 ters more and more freely and more cur- 

 rent flows through. By measuring the 

 amount of current we can follow the prog- 

 ress of death precisely as we follow the 

 progress of a chemical reaction in a test 

 tube. We then find that death is a very- 

 orderly process, following a definite law 

 which can be expressed mathematically. 

 These studies lead us to look upon the 

 death process as one which is always go- 

 ing on, even in a normal, actively grow- 

 ing cell. In other words we regard the 

 death process as a normal part of the life 

 process, producing no disturbance un- 

 less unduly accelerated by an injurious 

 agent which upsets the normal balance 

 and so produces death. The activity of 

 the cell need not cease with death but 

 may be merely changed in character. 



