CHAPTER IV 



INSTINCTS 



THE body of an animal may be likened to an 

 elaborate piece of clock-work which is driven by 

 a number of powerful main-springs lying con- 

 cealed within it. The surface of the machine 

 bears a number of little starting levers, each 

 adjusted to respond to the slightest touch and to 

 start the machinery by releasing a main-spring 

 that is connected with it. Some of the main- 

 springs are always, so to speak, wound up : an 

 unexpected crash will, for instance, make us start 

 at any time. Others become tense only at intervals : 

 if one is not hungry the sight of food is not attrac- 

 tive. Subject to this qualification an impulse is 

 directly and inevitably aroused by the sensation 

 that is connected with it. So considered, a living 

 creature closely resembles a machine ; and this is 

 the condition of an animal, such as an insect, which 

 is guided by directive instinct, when it is acting 

 under the influence of its instinctive guide. It 

 also represents the process by which our internal 

 organs perform their functions. The stomach 

 secretes its digestive fluids immediately it is 

 touched by food. 



But in the case of animals that are endowed with 

 memory we must expand our illustration. An 

 impulse may be aroused by a recollection as well 

 as by a sensory impression. The sight of a rat 



63 



