io8 HUXLEY MEMORIAL LECTURES 



know, forms part of a whole called the cerebro- 

 spinal nervous system, which, in addition to the 

 brain itself, comprises the spinal cord, the nerves, 

 etc. In the spinal cord are set up mechanisms 

 which permit the various parts of our body to 

 perform complicated and well co-ordinated move- 

 ments. These mechanisms may be set in action 

 without the intervention of the brain, under the 

 direct influence of an external stimulus; in such 

 a case, the bodily reaction follows immediately 

 on the stimulation. But there are cases in which 

 the external stimulus, instead of obtaining at 

 once, through the spinal cord, an appropriate 

 bodily reaction, goes up to the brain, in order to 

 come down again thence to the spinal cord, and 

 only then obtains from the cord the complex 

 physical movement. Why did it go to the brain ? 

 And what has it gained by this roundabout pro- 

 ceeding? A glance thrown on the general struc- 

 ture of the brain will answer these questions. 

 The brain is in communication with those 

 mechanisms of the spinal cord that we have just 

 referred to, and can send to any one of them the 

 order to work. Imagine a stimulation coming to 

 the brain from without, by the eye, ear or touch. 

 The brain is like a switch having the faculty of 

 putting the current thus received in communica- 

 tion with one or other of the motor mechanisms of 

 the spine, chosen at will. So that in sum, and 

 broadly speaking, the spinal cord is a storehouse 

 of ready-made complex actions, and the brain is 



