292 Prof. C. 8. Sherrington. [ Apr; cays 
observed not on stimulating the nerve trunk actually inoculated, but on 
stimulating the corresponding nerve of the opposite side. This result is in 
accord with expectation in view of the signs of the condition present. 
Conversion of inhibition into excitation by tetanus-toxin is demonstrable, 
as is that by strychnine, with the reflexes of the fore hmb as well as with 
those of the hind limb, and in the “ decerebrate ” animal as well as in the 
merely “spinal.” 
The fact that the very motor neurones, which are so regularly inhibited in 
the type-reflexes that have here been under examination, do under certain 
cortical stimulations exhibit excitation instead of inhibition, was a considera- 
tion which induced my search for the possibility in them of converting 
inhibition into excitation. This conversion of reflex inhibitory effect into 
excitatory having been obtained, it has been natural to enquire what 
difference, if any, is thus made to the reactions of the cortex cerebri. The 
material for doing so required a little time in preparation, but I am now 
able to report that the agents found to convert the spinal reactions do exert 
marked influence on those of the cerebral cortex. They transform the 
physiological topography of the motor cortex. 
It is, in my experience, quite exceptional to obtain primary extension of the 
opposite knee as a motor reaction from the cerebral cortex of the cat—or 
even, indeed, as a secondary movement. In exploring that cortex with 
unipolar faradisation I have often failed to elicit the movement at all 
throughout series of observations. Flexion, on the other hand, is regularly 
obtainable. This means, in hght of observations by H. Hering and myself, 
not that this cortex is in touch with the flexors alone, and not with the 
extensors, but that its usual effect on the latter is inhibition: the extensors 
are not unrepresented, but their normal representation is in the form of 
inhibition, not excitation, and thus, unless specially sought, escapes observa- 
tion. After exhibition of strychnine extension of knee becomes elicitable 
regularly from the cortex, and from the very points of it that yielded 
flexion previously. This conversion is, in my experience, not so facile as the 
conversion of the spinal reflex. The dose of strychnine has to be larger, or 
to operate longer. With doses additively given there is, early in the experi- 
ment, a period when reflex spinal inhibition of the extensors has been 
converted into excitation, but the cortex of the brain still yields knee- 
flexion, not extension. The cortical reversal has required in my hands doses 
that evoke convulsive seizures from time to time, and I have seen immediately 
after a severe convulsion the cortex either unable to evoke any movement 
of the knee or produce knee-flexion, though a short while before it gave 
knee-extension. 
