INTRODUCTORY : THE ANIMAL ORGANISM 15 



often brings into being new kinds of individuals, some of 

 which may be better fitted to live in the circumstances in 

 which the animal is placed. 



The consideration of reproduction in this connection 



shows clearly that the life processes are a unity. 

 The unity of The purposive character of life consists not only 

 Proceases. in the tendency of each individual act, but also 



in the way in which all the activities of the body 

 are interwoven so as to produce a single result. Each 

 process is related to the others. The incorporation of food 

 is in great part a preparation for disintegration. On the 

 other hand, much of the energy set free during^disintegra- 

 tion is spent in obtaining and making ready food for 

 incorporation. And in the long-run all the other life 

 processes, whether their immediate end be the avoidance 

 of danger, the increase of the substance of the body, or any 

 act subsidiary to either of these (such as the removal of 

 waste), are directed to the preparation and preservation 

 of the individual for reproduction, whereby the species is 

 continued. Thus all the activities of a living being combine 

 to continue the existence of its kind. 



In the foregoing paragraphs the living animal has been spoken of as 

 though its actions were calculable from a comparatively 

 Factor 8 * 01 "' 03 ' s ' m P li2 set °f factors. The student will do well to re- 

 member that this is far from the truth. Owing to a great 

 plasticity of constitution (p. 13), every individual has its own peculiarities 

 of behaviour, which depend on its past history. The two primary 

 things by which the course of the life processes of any animal is gov- 

 erned are: (1) the constitution of the animal, which sets up certain 

 "automatic" activities and permits the modification of these and the 

 starting of certain others ; (2) stimuli received from its surroundings. 

 Now the constitution is due in the first place to the tendencies with 

 which the animal was born, but, as we have already seen, it is due also 

 to external influences, which not only enable it to keep in existence 

 and develop along a hereditary path, but are also continually altering 

 it and thereby altering the behaviour of the animal. These influences 

 are never the same in any two animals, since no two can ever live 

 precisely the same lives. Thus, even if we suppose that two animals 

 are born with identical constitutions, they will not remain identical. 

 The consequence of this is that the history of the individual animal 

 is a factor in determining its behaviour. The burnt child dreads the 

 fire ; the actions of an athlete are quicker and more powerful than 

 those of an untrained man ; hardship may cause permanent enfeeble- 

 ment. Clearly, while the plasticity of animals may sometimes tend to 

 their undoing, it is on the whole beneficial, in enabling the individual 



