13 



Now if you decapitate a frog you may find a series of 

 reflex actions much more complex than these. If you 

 drop some acid on the thigh, the foot of the same side is 

 raised and attempts to rub it off. If you cut off the foot 

 the leg will attempt the same action, but, finding it im- 

 practicable the other foot will be raised for the same 

 purpose. If you remove the whole of the brain, but leave 

 the upper part of the cord or medulla intact, the animal 

 will still continue to live and breathe. It will also swallow 

 food. Sometimes human infants are born with only a 

 cord and medulla. Such a brainless creature will suck 

 and swallow as well as a perfectly formed child. The 

 medulla then is the great co-ordinating centre for swallow- 

 ing, for breathing, and indeed for many other actions. 

 Destruction of the medulla destroys the possibility of all 

 such movements and hence destroys life. Is this reflex 

 action conscious ? If you place a decapitated frog in water 

 and apply gradual heat, the frog wiU die without making 

 any attempt to escape, or manifesting the slightest incon- 

 venience. This rather tells against the supposition that it 

 is conscious in the sense in which the frog is a conscious 

 animal. And the fact that very complex mental opera- 

 tions often occur unconsciously — a fact to which I shall 

 have to refer farther on — natiu-ally associates itself in 

 our minds with the phenomena of reflex action. 



There is evidence to show that the optic thalami receive 

 and co-ordinate sensory impressions. Since the nerves of 

 special sense enter the optic thalamus of the same side, 

 while the nerves of general sensation cross over in the 

 cord, it is plain that disease of the optic thalamus would 

 affect the special senses of the same side, and general 

 sensation on tlie opposite side of the body. Similarly 

 disease of the corpus striatum paralyses half the face on 

 the same side, and the opposite side of the body. 



The fibres directly joining the optic thalamus to the 

 corpus striatum furnish a route for the adjustment of 

 movement to sensation without the nerve stimulus of 

 necessity going round by the cortex. 



Professor Ferrier has experimented on various portions 

 of the cortex by mild electrical stimulation. He has made 

 observations on monkeys and many other animals, and he 

 finds that in all the same parts of the brain have a special 

 importance in the performance of the same functions. Dr. 

 Ferrier has demonstrated that specific areas of the brain 



