6 FUNCTIONAL INERTIA 



are that it moves or secretes or produces heat, or ex- 

 ternal work or electric discharge or all of these together. 



Irritability is a general, primitive property 

 depending upon the biochemical configuration of 

 the excessively complicated molecules composing 

 protoplasm ( " biogens " of Verworn) a universal 

 property possessed by all living organisms, organs, 

 tissues, cells in both the vegetable and animal 

 worlds. Its existence is the essence and criterion 

 of life. The amoeba as well as the man has affect- 

 ability, the yeast-cell, the daisy, and the sensitive 

 plant all have it ; as a result of its possession, the 

 amceba engulfs the food particle or the poisonous 

 bacterium in contact with it, the man starts when 

 a gun is fired, the yeast-cell " ferments " sugar to 

 alcohol, the daisy opens to the morning sun and 

 closes in the dark, and Mimosa pudica folds its 

 leaves with a droop of inimitable grace. 



Environmental change or " stimulus " acting on 

 bioplasm possessing affectability, produces a result, 

 a phenomenon, a manifestation of irritability. 

 These several factors should be distinguished, and 

 each given its appropriate place or precedence in the 

 chain of causal occurrences. 



But we have not far to seek to discover mani- 

 festations of vitality or vital phenomena that can 

 scarcely be thought of as due to environmental 

 change acting on affectable protoplasm. 



When we apply a stimulus to a tissue and there is 

 no response for a time varying from T -J^th of a second 

 to several seconds, when we find in other tissues a 



