HOW THE BRAIN THINKS 



answers to a head and body, or root and stalk. The 

 leaves of a plant will turn towards the light ; so will 

 the head of a silk- worm. The parts take on special 

 duties and powers. And with this come the rudi- 

 ments of a nervous system. 



In worms and other lowly types, the different 

 parts of the animal are connected by thin threads 

 of a highly sensitive substance which conveys 

 a stimulus much more swiftly than the rest of 

 the body. They are nerves. When two or three 

 nerves meet at a common point, we have a little 

 bunch or bulb of nervous substance called a gan- 

 glion. It is usually found near the end which an- 

 swers to the head. Other ganglia appear as we 

 rise in the scale, but always the one near the head 

 is the largest, and it acts as a common centre for 

 all the others. It is the beginning of the brain. 



From this to the brain of a Helmholtz or a 

 Shakespeare is but a steady and uninterrupted de- 

 velopment, through fish and bird and beast to the 

 highly endowed ape, and thence, by insensible gra- 

 dations, to the finest type of civilized man. It is, 

 apparently, merely an increase in the number and 

 arrangement of the concerting units of ganglia and 

 connecting nerves. And in this orderly evolution 

 there is no break, no link missing anywhere. 



Whether it be the brain -cell of a glowworm or 

 one trembling with the harmonies of Tristan und 



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