32 Mr. J. N. Langley [March 14, 



nerve centre elsewhere in the brain. Further, when the cortex is set 

 in activity in a particular way by one impulse, another impulse 

 reaching it may inhibit the first activity, or, in terms of the localisa- 

 tion theory, one nerve centre in the cortex may send out inhibitory 

 imj^ulses to any other nerve centre of the cortex. 



I need not farther multiply instances of inhibition. I wish, 

 however, to lay stress on this, that it is highly probable that 

 impulses travelling from any peripheral nerve-ending to a nerve 

 centre, or from any one nerve centre to any other, may, under certain 

 circumstances, diminish or annul the functional activity of the nerve 

 centre, that is, may inhibit it. And there is equal reason to believe 

 that, under certain other circumstances, the effect produced will not 

 be inhibition, but an increase of activity of the centre. The exact 

 conditions which determine whether one effect or the other takes 

 place, have not as yet been made out. For the present the facts must 

 suffice us. We may now return to the mesmerised frog. 



Whatever the will may be, its action is accompanied by a certain 

 activity of the cortex of the brain ; if this activity is prevented from 

 taking place, the will can no longer act. From the physiological 

 standpoint, then, the mesmerised frog lies motionless because an 

 inhibition of a particular activity of the nerve cells of the cortex has 

 taken plaoe. We may distinguish two chief causes of this inhibition. 



The tactile stimuli sent to the central nervous system when the 

 frog lies on its back are obviously different from those sent when 

 the frog is in its normal position. The unusual nerve impulses 

 travelling from the skin in the unusual position of the frog are 

 inhibitory nerve impulses. There is reason to believe that they act 

 first on some lower centre of the brain, and that from this, impulses 

 are sent which diminish or annul the activity of the cortical nerve 

 ceils which is necessary for the exercise of will. 



The second chief cause of inhibition is in the cortex itself. 

 Handling the frog in the way which is done when it is mesmerised, 

 produces a certain emotional condition which we may call fright. 

 But when the animal is frightened, the nerve cells of the cortex are 

 set in activity in a special manner. This mode of activity inhibits 

 other modes of activity, and the will is paralysed.* We cannot at 

 present, I think, put in any more definite form the effect of one state 

 of the cortex of the brain upon its other possible states. We do not 

 know enough of the relations of the cortex of the brain to the 

 psychical functions to say more. In some cases fright seems to play 

 a very small 2)art, if any, in producing the effect. That it is not an 

 essential factor is, to some extent, confirmed by the fact that a frog 

 without the cerebral hemispheres can be easily mesmerised ; it is 



* The term " paralysis of the will " is here used to include the state in which 

 there is an effort of will, but in wliicli the effort is not followed by a despatcii of 

 nervous impulses from the cerebral hemispheres to the lower nervous centres. 



