156 INTRODUCTION TO SCIENCE 



behaviour; certain parts of the brain are corre- 

 lated with certain kinds of behaviour such as 

 speech; the health or the disease of the brain 

 is correlated withj the efficiency of behaviour. 

 There are numerous scientific data of this sort, 

 and they have nothing particular to do with 

 the metaphysical theory of "psycho-physical 

 parallelism." 



The scientific inquirer tries to fight shy of 

 the metaphysical problem of the relation of 

 body and mind, but, of course, in vain. He 

 will hold to the unity of the organism (thus 

 making a metaphysical assumption), and it is 

 the behaviour of the creature that he will partic- 

 ularly study. He can watch the dog and de- 

 scribe its behaviour; he can make experiments 

 to test its alertness, its memory, its power of 

 inference, and so on. In the case of birds, whose 

 eggs can be hatched in the laboratory, he dis- 

 covers what capacities are inborn and what have 

 to be acquired by learning. He can do all this 

 without getting into difficulties over the relations 

 of the dog's body and the dog's mind. The biolo- 

 gist prefers to keep to the dog. In this practical 

 monism he is confirmed by the philosophers who 

 make it clear that "body" and "soul" are equally 

 abstractions. "The severance of the original 

 unity of experience into a physical and a psy- 

 chical aspect is entirely a product of our own 



