190 CELL INTELLIGENCE THE CAUSE OF EVOLUTION 



These sensory centres are highly specialized portions of 

 the brain in which impulses from the end-organs of sense 

 are received and are usually worked up in consciousness 

 into the perception of an object, a sound, a thing in con- 

 tact with the skin, a smell or a taste. These centres are 

 specialized to receive, as the others are specialized to 

 emit. But it is quite clear that no centre can emit and 

 never receive. A sensory centre, in the first instance, re- 

 ceives and may for a time retain, but sooner or later it 

 transmits impulses either to an executive centre or to 

 another sensory centre. Thus when I see an apple, 

 impulses not only pass to the centre for vision, but on- 

 ward to the centre for taste, and from both these, impulses 

 can go over to the motor cells in the middle part of the 

 cerebrum, whence volitional impulses descend to the 

 muscles of the hand prepared to seize the fruit. That 

 this is the physical basis for the association of ideas 

 there is little doubt." 



To illustrate with a submarine, the end of the peri- 

 scope of the submarine, which is the same as the eye of 

 an animal, discovers a British ship in the distance, and 

 gives orders which will cause actions to take place, like 

 firing up the boilers, putting on more speed, twisting of 

 the rudders, etc. One activity will lead to another. Now 

 we shall give illustrations of the actions in case 'of some 

 local trouble or disturbance. Prof. Harris states : "We 

 get some grit into our eyes, and in consequence there is a 

 great outpouring of tears. We are not weeping, there is 

 no emotion calling forth tears, idle or otherwise, and we 

 have certainly not willed tears to flow. The lachrymal 

 glands have been reflexly stimulated to secrete. Clearly 

 there must be accessible to incoming stimulation some 

 specialized portion of the central nervous system, which 

 is set apart for inducing secretion in the tear glands, just 



