1895.] Impression*, $-c., to Voluntary Movement*. 97 



activity in the motor centres themselves situated in the spin al cord 

 by reason of which their molecular activity is so altered that they are 

 no longer capable of responding to ordinary volitional stimuli coming 

 from the cerebral cortex. This, at least, is the explanation that I 

 would suggest, instead of supposing, as the authors do, that volitional 

 power itself " has been absolutely abolished by the local loss of all 

 forms of sensibility " in the paralysed limbs. 



As I have already stated, a local loss of all forms of sensibility 

 caused by a lesion in the brain in the region of the internal capsule 

 causes no such paralysis. There is therefore no ground for sup- 

 posing that the animal's power of willing is interfered with by section 

 of all the posterior roots coming from the limbs ; while, on the other 

 hand, all the details furnished by Drs. Mott and Sherrington are 

 quite in harmony with the interpretation that the animal's ordinary 

 will power is unable to excite the spinal motor centres to action 

 when their molecular condition has been altered by cutting off all the 

 different stimuli proceeding to the corresponding region of the cord. 

 The immediate result of this may be presumed to be a lowering of 

 the habitual sub-activity of the motor centres upon which the con- 

 dition of tonus in the muscles depends. 



The fact that the results are produced only when all the sensory 

 roots are cut, and that "the defect in motility increases from the 

 attached base to the free apex of the limb," so that " the independent 

 and more delicately adjusted movements which employ preponderantly 

 the smaller and more individualised muscular masses of the hand and 

 foot " are those which are most severely affected or abolished, although 

 they may appear confirmatory of the interpretation of Drs. Mott and 

 Sherrington, are, in fact, no less in accordance with that here given. 

 This will be seen to be so if we bear in mind the overlapping of the 

 fields of distribution of the sensory roots in the spinal cord (as shown 

 by Sherrington), and the fact that the most delicate stimuli going to 

 the smaller muscles might be expected to be those which would prove 

 most impotent to rouse the sluggish spinal centres into activity. Again, 

 when the authors say: "We find, however, that forcible and rapid 

 movements, even of the fine joints at the end of the limb, can be 

 induced in the animals by causing them to ' struggle ;' for instance, 

 while recovering from ether inhalation or while trying to free them- 

 selves on being held awkwardly, the whole limb at all its joints may 

 exhibit movements," we have facts quite compatible with my inter- 

 pretation. Muscles may not respond to ordinary volitional stimuli, 

 and yet may respond when the stimulus is strengthened under the 

 influence of emotion. In a similar manner may we explain the fact 

 that when the kineesthetic centres corresponding with an apaesthete 

 limb are stimulated by electricity, movements of the previously 

 paralysed limb are produced just as easily as they are in a normal 



i 2 



