188 THE RIDDLE OF THE UNIVERSE. 



instruments of psychic activity that produce thought and 

 consciousness. In front we have the frontal brain or 

 centre of association ; behind, on top there is the vertical 

 brain, or parietal centre of association, and underneath 

 the principal brain, or " the great occipi to-temporal 

 centre of association " (the most important of all) ; lower 

 down, and internally, the insular brain or the insula of 

 Reil, the insular centre of association. These four 

 " thought-centres," distinguished from the inter- 

 mediate " sense-centres " by a peculiar and elaborate 

 nerve- structure, are the true and sole organs of 

 thought and consciousness. Flechsig has recently 

 pointed out that, in the case of man, very specific 

 structures are found in one part of them ; these 

 structures are wanting in the other mammals, and 

 they, therefore, afford an explanation of the superiority 

 of man's menta] powers. 



The momentous announcement of modern phy- 

 siology, that the cerebrum is the organ of conscious- 

 ness and mental action in man and the higher 

 mammals, is illustrated and confirmed by the patho- 

 logical study of its diseases. When parts of the cortex 

 are destroyed by disease their respective functions are 

 affected, and thus we are enabled, to some extent, to 

 localise the activities of the brain ; when certain 

 parts of the area are diseased, that portion of thought 

 and consciousness disappears which depends on those 

 particular sections. Pathological experiment yields 

 the same result ; the decay of some known area 

 (for instance, the centre of speech) extinguishes its 

 function (speech). In fact, there is proof enough in 

 the most familiar phenomena of consciousness of their 

 complete dependence on chemical changes in the sub- 

 stance of the brain. Many beverages (such as coffee 



