THE PHYSIOLOGICAL ASPECT OF MESMERISM. 803 



it will be better not to do so ; you suppress the yawn without moving 

 a muscle. What happens is this : An inhibitory nerve-impulse is sent 

 from the cortex, and jouts a stop to the indiscreet activity of a nerve- 

 center elsewhere in the brain. Further, when the cortex is set in ac- 

 tivity in a particular way by one impulse, another impulse reaching it 

 may inhibit the first activity, or, in terms of the localization theory, 

 one nerve-center in the cortex may send out inhibitory impulses to any 

 other nerve-center of the cortex. 



I need not further multiply instances of inhibition. I wish, how- 

 ever, to lay stress on this, that it is highly probable that impulses 

 traveling from any peripheral nerve-ending to a nerve-center, or from 

 any one nerve-center to any other, may, under certain circumstances, 

 diminish or annul the functional activity of the nerve-center — that is, 

 may inhibit it. And there is equal reason to believe that, under cer- 

 tain other circumstances, the effect produced will not be inhibition, 

 but an increase of activity of the center. 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 mesmerized 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 stand- 

 point, then, the mesmerized frog lies motionless because an inhibition 

 of a particular activity of the nerve-cells of the cortex has taken place. 

 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 traveling 

 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 

 center of the brain, and that from this impulses are sent which dimin- 

 ish or annul the activity of the cortical nerve-cells which is necessary 

 for the exercise of the will. 



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

 ling the frog in the way which is done when it is mesmerized 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 activ- 

 ity in a special manner. This mode of activity inhibits other modes 

 of activity, and the will is paralyzed.* We can not 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 part, if 



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

 an effort of will, but in which the effort is not followed by a dispatch of nervous impulses 

 from the cerebral hemispheres to the lower nervous centers. 



