38 IRRITABILITY 



this definition of stimulation for the research of life is evident. 

 Our whole experimental natural science always employs for 

 investigation of any state or process the same method : the state 

 or process to be observed is studied under systematically altered 

 conditions. By stimulating the living substance it is brought 

 under changed external conditions. A systematic employment 

 of stimulus is, therefore, the experimental means for the research 

 of life. 



