28 3Ir. J. N. LangJeij [March 14, 



stimulation, any one, or all of these nerve centres can be set in 

 activity. 



The second division of the central nervous system is the pos- 

 terior part of the brain — the brain minus the cortex of the cerebral 

 hemispheres. This, like the spinal cord, consists of a collection of 

 nerve centres, but the function of these nerve centres is much more 

 complex than that of the centres of the spinal cord. A stimulus to 

 the skin, which, when the spinal cord is the only part of the central 

 nervous system left, will produce either a local movement or no 

 movement at all, will, when the posterior part of the brain is also 

 present, produce a general co-ordinated movement such as occurs in 

 walking, jumping, swimming. In fact, all the co-ordinated movements 

 of which the body is capable can be brought about by the activity of 

 one or more of the lower centres of the brain. Moreover, these centres 

 can be set in action by events which have no effect when the spinal 

 cord only is present. Here a flash of light or a sudden noise sets in 

 activity a nerve centre in a manner strictly comparable to the way in 

 which a pinch applied to the foot sets in activity a nerve centre in the 

 spinal cord ; and just as in the spinal cord the active sensory centre 

 may excite to activity a motor centre, and this may cause the foot to 

 be moved, so in the lower centres of the brain the activity of the 

 visual or auditory centre may excite to activity a motor centre and 

 lead to a complicated movement such as shrinking or jumping, A frog 

 with these two divisions only of the central nervous system does 

 nothing of itself; it is without will and consciousness, in the same 

 way that the frog with a spinal cord only, is without will and con- 

 sciousness ; it is a complicated machine, any part of which can be 

 put in action by using the proper means. 



The last division of the central nervous system is the cortex of 

 the cerebral hemisf)heres. This part of the brain is concerned with 

 ideas, with will, and with consciousness in the sense in which that 

 term is usually employed, that is, speaking generally, it is con- 

 cerned with the higher psychical functions.* In saying that this 

 part of the brain is concerned with the higher psychical functions, 

 I mean that every higher psychical act is accompanied by some 

 definite change in the cortex of the cerebral hemisphere. I mean 

 that every emotion, every idea, every effort of will is accompanied 

 by an activity of nerve cells in this part of the brain and that 

 this activity is comparable to the activity which takes place in 

 definite cells of the spinal cord when a leg or arm of a brainless 

 frog is pinched. 



Here we touch the much disputed question of the localisation 

 of the functions of the brain. Eoughly speaking, this question 

 is whether there are nerve centres in the cortex corresponding to 

 those which exist in the rest of the brain and in the spinal cord : — 



♦ It is not possible within the limits of this lecture to give the reservations 

 that wonlrl be nccoHsary in a full discussion of the subject. 



