VITAL PHENOMEMA. I97 



this view. The opinion of the average man distrusts 

 it. It apph'cs the law of inertia only to inert matter. 

 This is because the vital response does not always 

 immediately succeed the external stimulus, and is not 

 always proportional to it. But it is sufficient to have 

 seen the flywheel of a steam engine to understand 

 that the restitution of a mechanical force cannot be 

 instantaneous. It is sufficient to have had a finger 

 on the trigger of a firearm to know that there is no 

 necessary proportion between the intensity of the 

 stimulus and the magnitude of the force produced. 

 Things happen in the living just as in the inert 

 machine. 



The faculty of entering into action when provoked 

 by an external stimulus has received, as we have said, 

 the name of irritability. The word is not used of 

 inert matter. However, the condition of the latter is 

 the same. But there is no need to affirm its irrita- 

 bility, because no one denies it. We know perfectly 

 well that brute matter is inert, that all the manifesta- 

 tions of activity of which it is the theatre are provoked. 

 Inertia is for it the equivalent of irritability in living 

 matter. But while it is not necessary to introduce 

 this idea into the physical sciences, where it has 

 reigned since the days of Galileo, it was, on the 

 contrary, necessary to affirm it in biology, precisely 

 because it was in biology that the opposing doctrine 

 of vital spontaneity ruled supreme. 



Such was the view held by Claude Bernard. He 

 never varied on this point. Irritability, said he, is the 

 property possessed " by every anatomical element 

 (that is to say, the protoplasm which enters into its 

 constitution) of being stimulated into activity and of 

 reacting in a certain manner under the influence of 



