INTRODUCTORY ; THE ANIMAL ORGANISM II 



thus no such connection with reproduction as is usually 

 found. 



The statements that have just been made deal for the 



most part with facts that are quite well known, 

 th re Lif 0nof an( ^ cover au tne activities of animals; yet 

 Processes: they do not give a complete picture of life, 



for they do not take into account the mean- 

 ing of the processes in which it consists. They give 

 no information as to why these processes take place 

 and what are their results. The characters that we have 

 so far considered in living animals are processes that 

 take place in their bodies. We have now to note certain 

 characters that concern rather the direction of these 

 processes. 



The most striking characteristic of a living animal is that 

 ii i bTiv '*■ res P on ds to stimuli. We can see this very 



clearly in considering our own lives. The 

 coming into sight of an enemy or a friend, of food or 

 some other coveted object, or of printed words, the sound 

 of the movement of wild animals, of an entreaty or a 

 command, or of music, the approach of some sub- 

 stance which can be smelt, the falling of a blow — such 

 changes in his surroundings as these constitute stimuli to 

 which a man, as we know, responds either by doing some- 

 thing which he had not been doing before or by ceasing 

 from something which he had before been doing. That is 

 to say, there occurs in his body a change which corresponds 

 to the change which has taken place outside him. It is, 

 indeed, of events which thus start, or are modified, in 

 response to stimuli that the life of man is made up. From 

 the first feeble cry that is drawn from his little body by 

 some discomfort in the world of chequered experience into 

 which he has been born, response is the most easily recog- 

 nised feature of his life until that hour when his dead lips 

 fail to answer his friends. The capacity for receiving 

 stimuli which start or stop in the body an activity of its 

 own is known as irritability. Two things must be noted 

 concerning the internal changes in which such activity 

 consists. Firstly, that their energy is derived, as we have 

 seen, not from without, as when a change is brought about 

 in water by heating it, but from within, as when a change 



