THE PSYCHIC DEVELOPMENT OF Y^UNG ANIMALS 265 



General Conclusions. 



In the dog, cat, rabbit (and in so far as the writer's 

 experiments go, in the rat and the mouse) neither the 

 brain cortex nor the underlying white matter is ex- 

 citable by electrical stimulation at birth or for some 

 days afterwards. 



The cortex is usually not excitable till about the period 

 when the eyes open, though there are exceptions to 

 this rule, most frequent in the writer's experience in 

 the cat, in favour of an earlier date. 



The white matter of the brain, just beneath the 

 cortex, is generally excitable, either at an earlier date 

 than the cortex, or with a weaker stimulus. 



The reaction for the limb movements is obtainable 

 invariably somewhat earlier in the dog and the cat, 

 and generally so in the rabbit, than those for the 

 neck, face, etc. 



Localisation for the cortex, and still more for the 

 white matter, is at first ill-defined, but gradually, 

 though rapidly, becomes more definite. 



In the cavy (guinea-pig) the cortex and the white 

 matter beneath are electrically excitable either at birth 

 or a few hours afterwards, and perfection of reaction 

 and localisation is reached in a few days. 



Before the brain cortex responds to electrical ex- 

 citation, ablation of the motor area (centres) leads to no 

 appreciable interference with movements. 



The younger the animal, the stronger the current 

 required to produce reaction up to the time that localisa- 

 tion is well established, i.e. the weakness of the current 

 required to cause a movement is an indication of the 

 degree of development of the centre in question. 



Differences for breeds and individuals exist and 



