THE PSYCHOLOGY OF ANIMAL PLAY. 289 



safely assume that strong feelings of pleasure accom- 

 pany it. 



And, further, energetic action is in itself a source 

 of pleasure. Experiments made with the dynamometer, 

 sphygmograph, pneumatograph, and plethysmograph 

 show that pleasure is accompanied by strengthened mus- 

 cular activity, quickened pulse-beat and respiration, and 

 increased peripheral circulation. It is not strange, then, 

 that the energetic activity of play with its analogous 

 physical effects is connected with feelings of pleasure. 

 P. Souriau says : " When we indulge in exercise that re- 

 quires the expenditure of much energy all our functions 

 are quickened, the heart beats more rapidly, respiration 

 is increased in frequency and in depth, and we experi- 

 ence a feeling of general well-being.- We are more alive 

 and glad that we are." * Very rapid and lively emotions 

 produce " a sort of intoxication and giddiness that are 

 most delightful." Besides these external effects of 

 pleasurable feelings they are accompanied internally by 

 a heightened excitation of the sensor and motor cen- 

 tres of the cerebrum, much like that produced by con- 

 centrated attention — a fact which points to the probable 

 explanation of the physiological side of pleasure by 

 means of the only purely intellectual play of animals, 

 curiosity. 



The unconscious connection of emotional accom- 

 paniments with intellectual activity is shown still more 

 clearly in that joy in ability or power which has con- 

 fronted us as the most important psychic feature of 

 play throughout this whole treatise. 



young animal, " because he has to try all the movements which it 

 is necessary for him to make in later life." 

 * Ibid. 



