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



be aroused to activity by slight exciting impulses. There is no 

 mystery in this, beyond the mystery which lies in the relative action 

 of all exciting and inhibitory impulses. The power of responding in 

 strikingly diiferent ways to weak stimuli differing in kind, or to stimuli 

 apparently of the same kind, but differing in intensity, is not peculiar 

 to the nervous system of man ; it is a jDOwer possessed by the nervous 

 system of all animals, and indeed, not improbably by all living 

 substance. This has already been touched upon in what I have said 

 of inhibition, but I will give you one or two other instances of the dis- 

 similar effects produced by slight, and apparently not very dissimilar, 

 stimuli, instances which are especially pertinent to the subject of 

 mesmerism. These we owe to Heidenhain. 



When morphia is given to a dog, and the animal is left undis- 

 turbed, it passes into a condition resembling sleep ; but a little 

 investigation usually shows that the condition differs in certain 

 notable respects from sleep. Whilst consciousness, as far as can be 

 told, is gone, and voluntary movement is abolished, many reflex 

 actions can be obtained much more readily than in the waking state ; 

 moreover, there is a tendency for the muscles which contract in a 

 reflex action to remain contracted, the nerve centres when set in 

 activity remain active for a considerable time, and continue to send 

 out impulses to the muscles, which in consequence are kept con- 

 tracted ; in other words the reflex contraction produced by a slight 

 stimulus applied to the skin is of a tonic instead of a tetanic 

 nature. Now this tonic contraction can be brought to an end by 

 various slight stimuli, for instance by lightly stroking the skin 

 over the contracted muscles, by gently tapping the contracted 

 part, by blowing in the face of the animal, or by stimulating 

 the cortex of the brain by a weak electric current. Nevertheless, 

 the acts just mentioned may, when the muscles are not contracted, 

 cause or help to cause, their contraction. I will give an instance of 

 this. Electrical stimulation of a definite part of the cortex of the 

 brain causes a tonic contraction of certain muscles of the leg, in con- 

 sequence of which, let us say, the leg is bent and remains so. Now wo 

 have seen that passing the hand over the skin of the leg will cause it 

 to unbend ; well, if the cortex of the brain be stimulated with an 

 electric current, not quite strong enough to produce of itself bending 

 of the leg, the bending may at once be produced by gently stroking the 

 leg at the same time as the cortex is being stimulated. Of a similar 

 nature is the effect of electrical currents of different strengths. 

 When a limb has been brought into a state of tonic contraction by 

 electrical stimulation of a certain part of the cortex of the brain, a 

 weaker electrical stimulation of the same spot of the cortex will bring 

 the tonic contraction to an end. 



The phenomena just described as occurring in a dog under the 

 influence of morphia, closely resemble those often observed in human 

 beings when mesmerised. Commonly in a mesmerised person the 

 arm, let us say, may be made to bend by gently stroking the skin over 



