INTRODUCTORY : THE ANIMAL ORGANISM 17 



1. Irritability — the starting or stopping in the body of 



an activity of its own as the result of the receipt of 

 a stimulus. 



2. Automatism — the starting or stopping of activity with- 



out an immediate external stimulus. 



3. Disintegration with liberation of energy, this energy 



appearing in various processes, of which the most 

 conspicuous are : 



i. Contraction, or change of shape, 

 ii. Chemical work, 



iii. Excretion and Secretion, the shedding out 

 from the substance of the body of chemical 

 products, 

 and possibly also in the Conduction of the 

 impulses which start these processes from 

 one part of the body to another. 



4. The Incorporation of food, which involves (a) the 



Absorption of new material, (b) the conversion by 

 Assimilation of unlike substances into the substance 

 of the body. 



5. Purposiveness — the direction of the activities of the 



body towards an end which concerns itself, namely 

 to its own preservation and that of its kind. This 

 is shown : 



i. as regards the individual, in the Struggle for 



Existence — the obtaining of food, and the 



avoidance or overcoming of enemies and 



unfavourable circumstances ; 



ii. as regards the race, in Reproduction — the 



bringing into existence of new individuals, 



which involves (a) the breaking off by 



Fission of a part of the body, and (b) the 



process of growth and structural and 



chemical change known as the Development 



of the part broken off. 



The relation of the life of animals to their structure is 



very clear in the light of what has just been 



KnotiS 1 ™ an " said - The animal body is a machine which 



reacts to events in the outer world in such a 



way as to prolong its own existence and that of its kind. 



Like other machines, it consists of a number of parts each 



