RESPONSIVE LIFE OF ORGANISMS 435 



modes of expression.* How we should express any emotion 

 if we had to do if, with a hydroid's tentacles, we cannot 

 conceive. 



Nevertheless, there is no living thing that lacks the 

 power of making visible response to the conditions of the 

 external world such response as no inorganic thing ever 

 manifests. This response may be slow, as in most plants, 

 or rapid, as in most animals possessed of parts having 

 specialized contractility; but it is always in evidence, and 

 in the last analysis it is the most distinctive characteristic of 

 life. Even growth and reproduction are but manifestations 

 of it. 



The capacity for responding to stimuli is, as we have 

 already seen, a property of protoplasm. When we watch 

 the streaming of protoplasm in a plant cell we may see it 

 accelerated or retarded with every change of temperature. 

 A little slime-mold plasmodium placed in a half lighted posi- 

 tion will move away from the light and into the shadow. It 

 will creep toward a decoction of dead leaves (its proper 

 food), and away from a solution of quinine. Such a bit of 

 naked protoplasm, therefore, although quite destitute of 

 organs, moves freely, and in a fundamental and important 

 sense it both perceives and acts. 



The behavior of organisms, which is-the visible manifesta- 

 tion of their psychic life, shall be the subject of our study in 



*"A bodily structure entirely unlike our own must create a 

 background of organic sensation which renders the whole mental 

 life of an animal foreign and unfamiliar to us. We speak, for 

 example, of an angry wasp. Anger in our own experience is 

 largely composed of sensations of quickened heart-beat, of altered 

 breathing, of muscular tension, and of increased blood-pressure in 

 the head and face. The circulation of a wasp is fundamentally 

 different from that of a vertebrate. A wasp does not breath 

 through lungs, it wears its skeleton on the outside, and it has 

 muscles attached to the inside of the skeleton. What is anger 

 like in the wasp's consciousness? We can form no adequate idea 

 of it." 



Washburn. 



