72 Can Science Explain Life? 



simplest protozoa under the microscope it seems 

 difficult to justify this conclusion on any sort of a 

 rational basis. The responsiveness to stimuli and 

 the spontaneity and arbitrariness of action upon 

 which mentality and self-consciousness are usu- 

 ally predicated are exhibited not only by the 

 nervous and muscular systems of the higher ani- 

 mals but also by the myoneme fibers of the uni- 

 cellular organisms. For example, if a vorticella 

 is touched the myonemes of the stalk will contract 

 and draw the animal away from the source of irri- 

 tation, just like the nerve and muscle fibers of a 

 higher animal will respond to the touch of a hot 

 object. The characteristic behavior of living or- 

 ganisms seems to be determined by the reactivity 

 of the protoplasm itself, which always possesses 

 substantially the same physical and chemical 

 properties regardless of the position of the par- 

 ticular organism in the scale of evolution. The 

 elaboration of protoplasmic structures into com- 

 plex anatomical systems does not change the in- 

 trinsic characteristics of living matter itself, and 

 in so far as mental attributes have their origin in 

 protoplasmic activity they must be regarded as 

 the common property of all forms of life. 



In the most highly developed forms of life men- 

 tality manifests itself in several different ways. 

 For example, it renders us conscious of sense per- 



