THE NERVOUS SYSTEM 307 



touched is that each hop, owing to the contact of the skin 

 with the ground, excites another hop ; the animal never 

 begins to move of its own accord. 



564. Function of the Cerebellum. The removal of the 

 whole of the cerebellum from an animal does not produce 

 death so long as the medulla is not injured, but the animal 

 becomes weak and unsteady in its movements. If the 

 cerebrum remains, the mental faculties are retained. Dis- 

 ease of the cerebellum in man produces dizziness and leads 

 to a staggering, reeling gate. Hence it is believed that 

 the function of the cerebellum is to aid the cerebrum in 

 the control of the muscles. It brings about proper co- 

 ordination of the muscular movements, so that in such 

 movements as standing, walking, talking, the different 

 muscles may each act at the right moment and with due 

 force. The spinal cord also coordinates movements. For 

 instance, if a frog is decapitated and left quiet for an hour 

 or two, so that the spinal cord may recover from the shock 

 due to the injury, it may be made to execute 'seemingly 

 purposeful movements. If a drop of acid be placed on the 

 flank of such a frog, the>leg will be drawn up and the acid 

 wiped off with the toes. But such coordinated move- 

 ments are not accompanied by consciousness. 



565. The Motor Area in the Brain (Figs. 204, 205, 206). 

 A wounded soldier was brought to the surgeons of the 

 German army with part of his skull torn away. The sur- 

 geons used an electric current to test whether the nerves 

 were paralyzed. They were astonished by finding that 

 whenever the electric current was applied to the wounded 

 part of the head, muscular movements were excited. It 

 was soon determined that by stimulating electrically a cer- 

 tain area of the cerebral cortex movements on the opposite 

 side, of the body can be excited. This area lies under the 

 parietal bone, and extends from the top of the brain to 

 the level of the ear. By experiments on monkeys and 



