224- ANIMAL AUTOMATISM v 



made upon the sensory nerves of the skin of the 

 frog by the contact with the water into which it 

 is thrown, causes the transmission to the central 

 nervous apparatus of an impulse which sets 

 going a certain machinery by which all the 

 muscles of swimming are brought into play in 

 due co-ordination. If the frog be stimulated by 

 some irritating body, it jumps or walks as well as 

 the complete frog can do. The simple sensory 

 impression, acting through the machinery of the 

 cord, gives rise to these complex combined 

 movements. 



It is possible to go a step farther. Suppose 

 that only the anterior division of the brain so 

 much of it as lies in front of the " optic lobes "- 

 is removed. If that operation is performed 

 quickly and skilfully, the frog may be kept in a 

 state of full bodily vigour for months, or it may 

 be for years; but it will sit unmoved. It sees 

 nothing : it hears nothing. It will starve sooner 

 than feed itself, although food put into its mouth 

 is swallowed. On irritation, it jumps or walks ; if 

 thrown into the water it swims. If it be put on 

 the hand, it sits there, crouched, perfectly quiet, 

 and would sit there for ever. If tin- hand be 

 inclined very gently and slowly, so that the fn-^ 

 would naturally tend to slip off, the creature's fore 

 paws an- shifted on to the edge of the hand, until 

 h' 1 i au just prevent himself from falling. If the 

 turning of the hand be slowly continued, he 



