178 THE RIDDLE OF THE UNIVERSE. 



entirely in harmony with his "book-keeping by double 

 entry." The materialists of the seventeenth and 

 eighteenth centuries appealed to the Cartesian theory 

 of the animal- soul and its purely mechanical activity 

 in support of their monistic psychology. The 

 spiritualists, on the other hand, asserted that their 

 dogma of the immortality of the soul and its 

 independence of the body was firmly established by 

 Descartes' theory of the human soul. This view is 

 still prevalent in the camp of the theologians and 

 dualistic metaphysicians. The scientific conception 

 of nature, however, which has been built up in the 

 nineteenth century, has, with the aid of empirical 

 progress in physiological and comparative psychology, 

 completely falsified it. 



II. Neurological theory of consciousness.— It is 

 present only in man and those higher animals which 

 have a centralised nervous system and organs of sense. 

 The conviction that a large number of animals — at 

 least the higher mammals — are not less endowed than 

 man with a thinking soul and consciousness prevails 

 in modern zoology, exact physiology, and the monistic 

 psychology. The immense progress we have made 

 in the various branches of biology has contributed to 

 bring about a recognition of this important truth. 

 We confine ourselves for the present to the higher 

 vertebrates, and especially the mammals. That the 

 most intelligent specimens of these highly-developed 

 vertebrates — apes and dogs, in particular — have a 

 strong resemblance to man in their whole psychic 

 life has been recognised and speculated on for thou- 

 sands of years. Their faculty of presentation and 

 sensation, of feeling and desire, is so like that of man 

 that we need adduce no proof of our thesis. But even 



