384 REFLEX ACTION, INSTINCT, AND REASON 



sleepy, we instinctively, without learning, place ourselves in an 

 attitude of rest. Doubtless we learn in time what attitudes are 

 most comfortable, but no learning is needed to secure cessation 

 of movement and relaxation of all our voluntary muscles and the 

 consequent assumption of a restful position. 



637. Hunger and thirst are terms which are applied both to the 

 instinctive desires to take food and water and to the antecedent 

 sensations which awaken them. Thus, when we say we are 

 hungry we may mean either the feeling of discomfort in the region 

 of the stomach, or the wish for food, or both. The recognition of 

 food as such by the sense of taste is also instinctive. Normally 

 we eat and drink only nutritive substances, those which contain 

 food or water, with pleasure. Probably, however, this instinct is 

 more perfect in the lower animals than in man in whom it seems 

 to have undergone some retrogression. The infant, protected as 

 it is by its mother's intelligent care, tends to swallow any small 

 object that comes to hand ; the caterpillar and the puppy, which 

 is aided by its sense of smell, are rarely in fault. In all animals 

 the amount of food desired is limited by the needs of the individual, 

 though even in this case the instinct appears more perfect in the 

 lower animals than in man. Instinctive also are those voluntary 

 movements of tongue and jaws which occur when food or water 

 is placed in the mouth. Unlike the caterpillar, however, man 

 must learn all those actions by means of which he procures 

 food. 



638. The impulse to play is an instinct, but it prompts to no 

 action for which our muscles are instinctively co-ordinated. Its 

 sole function is to impel us to make physical and mental acquire- 

 ments. Under its influence we use our bodies and minds which 

 develop in response to the stimulus thus supplied till we are fitted 

 to the ancestral environment We have already dealt at length 

 with physical use-acquirements. 1 The mental acquirements 

 resulting from play are strictly homologous and not less important. 

 They enable us to co-ordinate our muscles for purposeful action 

 and so perform our voluntary actions as swiftly and surely as 

 reflexes. The vague movements of the infant become purposeful 

 if awkward ; his awkward movements become easy and sure ; and 

 these easy movements at length become ' automatic.' Only those 

 animals sport which make physical and mental acquirements, and 

 they sport only when play is useful, and in a way that is 

 useful. The caterpillar does not sport ; he has no physical and 



1 See chapter i. 



