Psychology, as an experimental science, is only about 

 fifty years old, but already it is beginning to provide some 

 highly significant information on the nature of processes 

 taking place in the brain, and which are associated with 

 behavior: the fundamental processes of thought in the 

 higher animals are at last, after centuries of inconclusive 

 discussion, being brought into the field of rational in- 

 vestigation. 



The first successful psychological experiments on ani- 

 mals were those of Pavlov (1879-). Pavlov used dogs as 

 experimental animals in his investigations of the mecha- 

 nism of learning. It was already recognized that there ex- 

 isted a number of natural reflex mechanisms in animals, 

 the purpose of which was to protect the animal from injury: 

 e.g. when the extremities of the limbs encounter a hot 

 surface, the limb muscles contract rapidly to remove the 

 end from the injurious temperature. This mechanism is 

 automatic, not involving any learning process, and the 

 actual sequence of physiological events is quite straight- 

 forward: Heat receptors on the limb extremities generate 

 nervous impulses on being heated, which travel along 

 the long sensory nerves up the limb into the spinal cord 

 where they pass across nerve junctions (synapses), setting 

 off further impulses in other (motor) nerves going to 

 muscles in the limb concerned, and so causing these mus- 

 cles to contract and move the limb away from danger. 



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