THE PSYCHIC DEVELOPMENT OF YOUNG ANIMALS 161 



I have noticed in these and other puppies a quick 

 recognition of human association through what I have 

 termed the lip-call, not to be identified with any other 

 sound. Is this the result of heredity to any extent, 

 this sound having been used more than any other in 

 attracting the attention of dogs ? But so readily are 

 psychic associations formed that one must not be sure 

 of this. The dog, above all our domestic animals, is a 

 plastic creature, and his life is made up largely of 

 associative reflexes and kindred neuroses with corres- 

 ponding psychoses. This principle I regard as a key 

 that unlocks more of the secret places of canine 

 nature than perhaps any other, unless it be heredity 

 itself. 



HUMOUR. The records of the 26th and 33rd days 

 seem to show that even such young puppies appreciate 

 fun or humour, much as a child does, and this can be 

 almost daily observed in mature dogs. 



ATTENTION AND FATIGUE. My observations on these 

 subjects, some of which I have attempted to record, 

 show, in the plainest way, how very readily a puppy is 

 fatigued, but also indicate a gradual improvement in 

 this respect. This readiness in experiencing fatigue 

 explains why, moreover, one observer may be led to 

 question the observations of another on very young 

 animals. Again and again have I failed in my attempt 

 to get the same result on repetition. In fact, the rule 

 up to about the 20th day was, that success on repetition 

 of certain stimuli was very doubtful owing to fatigue. 



This is well illustrated in the case of the growling 

 reflex, etc. of the 17th day, but it applies to all the 

 senses and the whole life of the animal, somatic and 

 psychic. 



For this reason sleep follows at once on the exertion 

 of play, with its physical movements and its sensory 

 stimuli tending to exhaust. 



